Izuku kept wary of any guards that might question where he was going, using the coral forest that grew in abundance in the castle grounds to hide whenever someone drew too close. He mentally cheered to himself as he slipped outside the castle grounds and darted through the city streets, calling out apologies whenever he bumped into someone in his haste. Even without an invisibility potion, he was getting better at sneaking!

Leaving the barrier that protected the city behind, Izuku dug a hand into the pouch strapped to his waist, prying out the wooden coin that All For One had gifted him last time to protect him from Nomu. He figured it must be a charm or amulet that had been enchanted to keep them at bay or make him invisible to their sight. Though he'd been studying it for days and he still hadn't found the slightest trace of magic, making it difficult for him to have confidence. He clutched it tightly in his hand, his fins fidgeting nervously as the coral highlands drew closer and closer, keeping his eyes sharp for the monstrous Nomu.

And along the edges of the greying reef he spotted one, watching him with its sharp, glowing eyes, fidgeting and digging its claws into the stone. Izuku tensed, ready to swim for his life if it moved to attack him.

Yet it stayed in place. It simply stared at him, twitching in place and gnashing its fangs, as though impatient for something, but never moving from its perch. Hesitantly, Izuku swam closer, clutching the coin close to his chest as he swam downward.

"Ah!" Izuku yelped when a black scaled hand swiped at the water from a depression in the coral he hadn't been aware of when looking from above. He slapped his tail against the offending arm as his heart pounded in his ears. His chest heaved as he spotted another Nomu, curled in the crevice. Izuku flinched away when its fangs snapped rapidly with a clicking sound, terror nearly overwhelming him when it reached a hand out towards him, talons flashing in the dimming light.

Only to stop in place, drawing back with a keening whine and clutching at its skull, eyes narrowing as though pained by something. It turned its back to Izuku, withdrawing deeper into the dark space until Izuku couldn't make out its form any longer.

Izuku exhaled a relieved sigh, some of the tension leaving his body. The coin worked as All For One said it would!

Even so, he was mindful as he carefully moved down again, not wanting to startle or alarm any more that might be hiding within the coral. A good thing too, as he spotted a few more along the way, either resting on the edges of the reef, their scales grating against the stone with an ear-piercing screech, or swimming further out near the ocean floor, darting between rocks whenever they noticed him looking at them. He even spotted one burrowing into the sand, and if Izuku hadn't known better he would have assumed it was just one of the many dunes littered about.

He knew All For One was strong enough to keep himself safe, but it didn't stop worry from creeping up on him. Where did all these Nomu come from anyway? Why were they only now showing themselves? Were they migrating from another part of the ocean? It was concerning.

"All For One?" Izuku called out on entering the den, but found he didn't need to, spotting the Cecaelia sitting by his desk, his focus entirely on a datapad. Until his head turned at Izuku's voice. He raised a curious eyebrow at Izuku.

"Back again, guppy?" All For One hummed, flicking through the datapad before setting it down, sitting up from his chair and swimming to the cabinets. He grabbed a vial from an upper shelf while his tentacles pried a couple jars from the bottom. He swam over to a bubbling cauldron, placing the ingredients he procured into the shimmering surface in pinches and chunks. Izuku watched in amazement as the purple hue shifted into glossy black sheen, looking like oil. He couldn't help but wonder what it was for.

"Y-Yeah." Izuku nodded, prying out the vial containing the latest ingredient, holding it out for him to take. A smile worked itself onto his face when All For One took the bottle, seeming intrigued as he observed the droplet inside. "I got the human tear you asked for!"

"Already?" All For One mused. His normally stern expression eased, the tiniest smile Izuku had ever seen tugging at the Cecaelia's mouth. His voice softened. "You continue to impress me, little one."

Warmth filled Izuku's heart, beaming at this approval.

"Thank you!" Izuku said, watching as All For One carefully put the tear away into the cabinet. "I, um, I'm sorry I doubted you before though. About humans I mean. I didn't really believe it when you said they actually existed. I was so surprised when I saw one of their ships floating on the surface!"

All For One tousled the curls of his hair with a chuckle as he swam by, pausing to stir the mixture in the cauldron once. "There's a lot you don't know about the world, little one. There's so much more beyond the barriers that protect your kingdom."

"Yeah. There's so much I want to see!" Izuku nodded in agreement. "But I…I can't really leave the castle without permission because I don't have…you know."

"Yes, I imagine your father is quite protective of you due to your…disability," All For One hummed in understanding. "Though it seems to be without cause, as you have proven yourself to be quite capable."

Izuku felt his face redden, not knowing what to say at such praise, tail fidgeting awkwardly.

"But I do find myself curious," All For One admitted, glancing at him while tending to his potion. "How is it you acquired the tear so easily? I had thought it would have taken you a month, at the very least for this one, due to the distance."

"Oh, that wasn't very hard!" Izuku admitted, sinking to the sandy floor of the cave and huddling closer to the vent that heated the cauldron, the warmth pleasant against his scales. "There's a mirror in the throne room that allows members of the royal family to teleport great distances for a period of time. The hard part was finding the ship and keeping up with it really."

"Ah, I see," All For One hummed. "I assume you managed to pry a human off the ship then? Did you cut them with the fins along your forearms to force them to shed a tear?"

"No, not at all! I don't want to hurt anyone, certainly not for selfish reasons." Izuku shook his head, curling in on himself. "I found a human leaning on the deck of the ship, and he was upset because of…issues…with his family. He shed a tear and I managed to catch it."

All For One tilted his head slightly. "Oh? Did you speak with the human to learn that?"

"I-I did. Was I not supposed to?" Izuku asked, suddenly afraid that it might have been a taboo to speak with a surface dweller.

"No, it matters not. I'm more surprised he didn't try to capture you on sight, if anything. Humans are infamously greedy creatures. They always want more than they can afford to pay."

"He didn't try to capture me or anything!" Izuku defended, head rising from his arms. "He fell overboard, and I rescued him when he couldn't swim!"

All For One huffed with laughter, shaking his head in amusement. "How typical of a human."

"But yeah," Izuku continued on. "He was pretty nice about me taking his tear. All he wanted was a scale in return. I think that's a pretty fair trade, all things considered."

"It'll be his family heirloom for generations to come," All For One chuckled. "Humans have always held a fascination with mers and sirens."

"Have you met a lot of humans then? If you know so much about them?" Izuku asked, curiosity piqued.

"Many, many times," All For One confirmed, swimming across the room once more and opening a box that radiated a chill when it opened. He frowned, searching through its contents as he continued to speak. "I've been all across the world, and if humans were in the area, they always sought me out in the hopes I would fulfill their desires and dreams."

"And you did, right?" Izuku asked, curling closer to the vent with a shiver when the chill traveled through the cavern. "You helped them like you're helping me now?"

"Oh yes." All For One nodded in confirmation. A toothy grin pulled at the Cecaelia's lips in a self satisfied way. "That is what I do, after all. It's what I live for." He sounded very pleased with himself. Izuku couldn't blame him though; helping people always made him feel happy too.

"So…Can you turn a human into a mer?" Izuku asked.

"Of course," All For One waved a hand dismissively, as if asking such a question was offensive to his capabilities.

"Really?"

"Indeed. You'd be surprised at how many humans have asked that of me over the years. It's grown quite tiresome, actually." All For One huffed. "I suppose they recognize that we are their betters."

"Oh…" Izuku wondered if he shouldn't have discouraged Shouto. But he still thought Shouto had been seeking out a transformation for the wrong reasons, even if he would look great with a tail. "What would you ask for in return then?"

"It varies from person to person, but considering the complex nature of the magic involved the price is quite high. Most can't afford to deliver on their end of the bargain after I've fulfilled mine. In such cases, they become indentured servants, as stated by the contract they agreed upon when finalizing the deal, until I declare their debt paid in full."

"Oh…It must have been awhile since you've dealt with a human then huh?" Izuku surmised, as he had not seen any former human mer about.

"You can say that, I suppose." All For One chuckled. Before Izuku could ask what he meant, he closed the box after he had pried out what he was looking for: a couple of pieces of fish, descaled and deboned, ready for cooking. All For One skewered the pieces with a rod of metal, and Izuku blinked when one was held out for him.

"You're probably hungry after your adventure, are you not?" All For One stated. "You can cook it over the vent."

"O-Oh," Izuku stammered, having not even realized how hungry he was in all the excitement. He took it from Cecaelia, holding it above the heat of the vent, a sizzling crackling through the water. "Um, thank you."

"My apologies for not having a meal suitable for a prince," All For One said as he prepared his own skewer of fish.

"Oh, no, it's fine!" Izuku assured him quickly. "But is it really okay for you to share your food with me? I have plenty at the castle, while you're out here all alone…"

"Don't worry about me, guppy," All For One chortled, offering an amused smile. "I'm perfectly capable of taking care of myself."

"Are you sure?" Izuku insisted, feeling a little guilty. "I can bring you food from the city if you'd like? Anything you want!"

"I'm fine, I assure you," he said. "But thank you."

"If you're sure…" Izuku bit at his lip.

"There is one thing you could bring me." All For One's eyes briefly seemed to gleam with red light. "The final ingredient for the transformation ritual."

Izuku's pulse sped up and his tail twitched. Just one more ingredient left! He was so close to having magic! Then he would finally be considered a worthy prince!

All For One said, "I need the king's trident."

Izuku froze. "I-I can't. That belongs to my father. I can't steal his most cherished possession. It's a royal artifact. Please, isn't there anything else I can give you?"

All For One sighed. "I thought you wanted magic badly. You'd do anything, you said."

"But not hurt someone else! Why would you need a trident as an ingredient in a spell? That makes no sense. It doesn't have resonance with me, only my father." Izuku frowned. "You were able to give magic to Aoyama. What ingredients did you use then?" There was only one trident so it couldn't have been required last time.

All For One leaned forward, the water swishing around him and his gaze intense. "The ruby in the pommel of the trident contains a bit of my power. I gave it as a gift to my late brother, but it was lost long ago. In order to craft a spell so powerful as to give you magic, I need my full power back. Helping the Aoyama boy drained me. I wouldn't be able to cast another such spell for a full decade. Not unless I get my magic back."

A decade! Izuku couldn't imagine waiting that long. No one would take him seriously as a prince if he couldn't become a warrior much sooner than that. "Then, you only need the ruby, not the whole trident?" he asked slowly.

All For One shrugged half a dozen tentacles. "The ruby is rightfully mine. I only need that part of the weapon, because it has my power. The magic wouldn't do a mer any good, but it's an important part of me. It's also the very last remnant of my little brother."

The trident was a family heirloom, but the gemstone could be replaced. There were plenty of rubies in the royal treasury. Yet stealing still didn't sit right. Izuku gnawed on his lip. "The ruby rightfully belongs to you? How did you lose it?"

All For One said, "I was unable to find it after my dear little brother died. It was likely taken by his killer. Somehow it made its way to your family. Mers are prone to looting Cecaelia dens and stealing our belongings. We're only seen as monsters, after all. Killing a monster and running off with their belongings is positively heroic!" His tone turned bitter and sour.

Izuku squirmed, knowing there was truth to Cecaelia's words. If the ruby had been stolen, then it would be a good deed to return it to its rightful owner. Still he hesitated, teetering on the edge of making a decision. "I don't mean to be rude, but can you prove that the ruby should belong to you?"

All For One raised an eyebrow. "I take no offense. It's a reasonable question, and you're a clever and inquisitive child." He swam over to a drawer and pulled out a datapad. Returning, he said, "This is Yoichi, my younger brother."

In the picture, a younger Cecaelia with white hair and green eyes smiled brilliantly. He wore a golden chain around his neck with a ruby. Izuku recognized the same ruby from his father's trident, because it had a distinct dent on the side. All For One gazed down at the picture, and Izuku nearly lost his breath at the pain and sorrow in the Cecaelia's eyes. Izuku looked away, feeling as if he was intruding on a private moment.

"He was so young when he died," All For One murmured. "Barely more than a child, by Cecaelia standards. Too young to swim the seas on his own, but I…I failed him."

"You mustn't think like that. It wasn't your fault," Izuku said, offering the cliched words of comfort automatically. The weight of the Cecaelia's grief made his eyes prickle with sympathetic tears. He held them back, feeling that it wasn't his place to make this about himself.

All For One held out the necklace around his neck. It was clearly the same golden chain that Yoichi had worn, and in the center, there was an empty space where a gem had clearly been pried away from a pendant.

Izuku swallowed. Then he bowed his head. "On the behalf of the royal family, I'm very sorry for this theft. I'll return your ruby to you. I give you my word as prince."

"Of course you will, you want your magic," All For One said.

Head still lowered, Izuku insisted, "That's not the only reason. It belonged to your brother, it's rightfully yours. I'm sorry. I would get it back for you even if you didn't give me magic afterward."

Izuku felt a hand card through his curls. All For One was patting his head. He looked up. In a surprisingly gentle voice, the Cecaelia said, "You'll have your magic. I promised, and I always keep my bargains."

"Oh, thank you!" Izuku had meant what he'd said, but he still wanted his magic very much.

As Izuku swam away, he tried to think. Could he swap out the ruby for another one without his father noticing? No, that wouldn't work. He didn't have enough knowledge of metalworking to replace the stone, or the correct tools. His father would notice if his trident went missing for days.

Could Izuku explain the truth? His father was a good person, surely he wouldn't want to keep stolen property. The royal family must have purchased the ruby without knowing of its sordid origins, taken from the dead body of a young Cecaelia possibly murdered by the thief.

But when Izuku pictured trying to explain the situation to his father, he saw no way around admitting that he'd been sneaking out of the palace. He'd get in so much trouble. He'd be carefully watched after that. And if his father chose not to believe him about the opportunity to get magic, then he'd never be let out of the palace and he'd lose his last chance.

There was no way around it. Izuku would have to steal the ruby.

King Toshinori sat at his desk, looking through datapads, when his son knocked on the door. "Dad? Do you have a moment?"

"Of course, always for you!" Toshinori's head shot up. He'd been nervous to speak to his son after their argument. The last couple times he'd come by his son's bedroom, the door had been locked and Izuku had refused to answer. Toshinori had been torn between giving him space as he'd requested and fatherly fears. Could Izuku be extending a peace offering now?

Izuku fidged. "I'd like to practice martial arts with you. Just like we used to, when I was young, and…before I found out that I didn't have magic."

"I would be delighted." Toshinori leapt up, dropping his datapad. He didn't bother to pick it up. Surely this meant Izuku wasn't angry at him any longer, and it would be a chance to find out what his son had been up to lately. It seemed like Izuku's lack of magic had been bothering him more than Toshinori had realized. "I'm sorry I haven't had as much time to train with you lately. There have been more issues popping up around the kingdom. I've been dealing with a dangerous enemy resurfacing." He'd also gotten sicker, making it harder for him to spar on a regular basis, but he didn't want to worry his son. "It has nothing to do with your lack of magic."

"Sure." Izuku looked away.

There was definitely a matter to be discussed, there. Toshinori felt a tickling in the back of his throat. He'd had a splitting headache all day. This was one of the days when his illness acted up. Truthfully, he was in no condition for heavy physical activity. But he couldn't turn down his son. Clearly Izuku would be convinced it was because of his lack of magic if Toshinori made excuses.

As they swam down the hallway, Toshinori noticed his son had a thin, scabbed-over cut on his tail. "Izuku, what happened to your tail?"

"That?" Izuku looked down. "I bumped into a table."

It looked more like a claw mark. "Have you been sneaking out again?" This was the scale that broke the orca's back. "We talked about this. I'm going to assign young Bakugo to follow you around."

"Yeah, I knew you'd act like this if I tried to talk to you," Izuku grumbled.

Toshinori winced. This reaction was somehow even worse than the argument he'd expected. It felt like Izuku had given up on him. "You can still take guards with you to the market. Did you have a reason for leaving besides potions ingredients?"

"Whatever," Izuku muttered, swimming through the doorway.

The royal family had a private gym to themselves, with a ring in the middle for sparring. Toshinori went to the weapons rack, reaching for a padded wooden sword.

Izuku said, "I'd hoped that you'd spar with me using your trident."

Toshinori froze. "That would be too dangerous."

"Because I don't have magic?" Izuku demanded, his eyes blazing.

"No, because it's an edged weapon!"

"If I had magic, then I could cast a spell to dull the tips." Izuku crossed his arms. "It's because I don't have magic. Fine, if you don't want to spar, then I'll leave." He started to swim away.

Were all teenagers like this? Toshinori wished Inko were here, so he could consult with her. "Wait! I'll cast a spell on my trident to make it safe." Safer, at least. Even if Toshinori used magic to pad the tips, it was still a heavy weapon. He'd have to be very careful not to fight at full strength and actually hit his son. Perhaps he could let himself be disarmed right away. Izuku seemed like he needed a win.

Izuku took a practice sword off the rack. His eyes grim, he took his position in the circle. "One, two, three, begin."

Immediately, Izuku lunged forward. His thrust was strange–instead of trying to hit Toshinori, he seemed to be trying to hit the trident.

Toshinori easily blocked. He did not try to retaliate, too worried about hurting Izuku. "How have you been lately? Can you tell me why you've been leaving the palace? I'm only worried about you."

Izuku retreated and circled him. "Why shouldn't I go outside when I please? Other mers don't have to stay cooped up at home. I know you don't take me seriously because I don't have magic, but I can craft potions as weapons. I chased off a shark recently!"

"You what? When did you face a shark?" Toshinori nearly dropped his trident in shock.

Izuku took advantage, darting forward. He could have easily struck his father, but once again, he hammered at the trident, right at the pommel. "You'd let Kacchan face a shark, but not me! Because you think I'm weak!"

"Actually all the guards are supposed to avoid fighting sharks. Izuku, this isn't because you don't have magic. An ancient, dangerous enemy has been lurking around the kingdom." Sweat dripped down Toshinori's forehead as their weapons locked. He'd never realized his son felt like this. Should he have told Izuku the truth sooner?

"An enemy?" Izuku asked with a mocking lilt. "Why haven't I heard about this?" He ground down his sword harder, against the pommel.

"Because I was worried about you!" Toshinori cried. A cough bubbled up in his throat. He felt horribly sick. He could barely remain upright. This sparring match had been a mistake.

"Because you think I'm weak!" Izuku struck again. The trident fell from Toshinori's hands, and the ruby popped out of the pommel. The impact knocked Izuku's sword out of his hand too, and his glove fell off.

"Sorry, Dad!" Izuku said, a little too quickly. He darted forward and picked up the ruby. "Oops, I broke it! This ruby has a dent now. We'll have to get a new one for your trident. I'm really, terribly sorry. It was a total accident." He slipped the ruby into his pocket.

But Toshinori barely paid attention to the broken trident, because he'd seen a single black dot on his son's palm. No, no, no. That monster couldn't have possibly gotten his tentacles into his child. Izuku was supposed to be safe in the palace. Surely Toshinori couldn't have failed his wife this badly. Hoarsely, Toshinori said, "Izuku, please tell me that mark isn't what I think it is. Please tell me that you haven't struck a deal with All For One."

Izuku's eyes widened, and the guilt on his face said everything. Then he bolted for the door.

Toshinori lunged forward to grab his child. But then a cough erupted from his throat. His vision swam and doubled. Blood spurted from his mouth. He fell to the floor. With a shaky gasp, he reached out his hand, but darkness had already fallen over his eyes, then he saw nothing more.

Izuku didn't stop even once when fleeing the castle and the city, forgoing all stealth in his mad dash towards the reef with the ruby, not even pausing to apologize to those he bumped into or to catch his breath.

His father had discovered his mark binding him contractually to All For One. Somehow Toshinori knew All For One. And the look of rage on his father's face had sent a bolt of terror and wretchedness straight to his heart. Without a doubt, Izuku knew that his father would stop at nothing to prevent him from seeing All For One and delivering the ruby to fulfill his contract.

A tumultuous mixture of guilt and anger bubbled inside him. Guilt at having stolen from his father. At leaving him behind. At the expression of shock he had worn. But he was so close now to having magic of his own, and he couldn't let anyone, not even his own father, stop him from achieving his goal. Izuku had foolishly thought that his dad might even be proud of him for going to such lengths to prove himself, that he was stronger and more capable than everyone had thought him to be.

But no. His father had tried to stop him. And so Izuku had fled with a heavy heart, never once looking back.

Once he had magic his dad would understand, Izuku told himself. Once he had magic, everything would be as it should be. He would be a better son and prince. He could learn how to fight like everyone else and be able to fulfill his duties as the heir to the throne. People would no longer look down on him for being magicless. He would be normal.

He would no longer be a stain of disappointment on his father.

Why didn't his father believe in him? Why did he always try to stop him whenever he wanted to better himself? He never allowed Izuku to train with the others, never allowed him to leave the castle without a guard, never once had faith in his dreams.

Unlike All For One. All For One who let Izuku prove himself and show that he wasn't a useless, pampered prince who needed to be holed up in his castle. Who praised and encouraged him for his successes and never tried to dissuade Izuku from pursuing his goals.

Izuku brushed away the sting of tears that burned in his eyes, willing himself to move even faster the closer he grew to the reef, his heart hammering against his ribs. Too quickly, it turned out, as his arrival startled the many Nomu laying in wait among the greyed reef and the sandy bottom, their sharp, jagged fins flaring in warning with a series of growls and snarls, mismatched yellowed fangs gnashing.

But their riled states soon soothed after a moment, laying back down with only slight agitation. This allowed Izuku to safely approach, swiftly swimming into All For One's abode. He did wonder why they looked at his face, not his protective talisman. The ruby in his hand almost seemed to glow, and he clutched it tightly.

Inside the cave, All For One's back was turned away from him, magic twisting through the water in flashes of red and black electricity. They dissipated into glowing spheres of stardust that drifted downward. He was tending to something on the far side of the cavern, more secluded than the open center.

Izuku opened his mouth to call out to the Cecaelia, but he didn't have time to speak even a word before All For One turned to face him, not seeming surprised by his arrival at all. A warm smile graced his features, which only seemed to widen when he caught a glimpse of the ruby in his hand.

"I had a feeling you would be arriving soon," All For One said, swimming closer. "You really are a remarkable and talented little mer to have gathered everything so quickly and efficiently."

"T-Thank you," Izuku stammered, holding out the ruby towards All For One. Only a second passed before it was snatched out of his hand, startling Izuku. Something gleamed in All For One's eyes as he stared at the stone, his gaze growing softer. All For One clutched it close for a moment, then reached for his necklace. The ruby slotted into place into an empty socket perfectly, and a weight seemed to lift from the Cecaelia's shoulders. Izuku blinked when All For One turned his attention back to him, a soft smile that was beyond relieved on his face.

"I should be the one thanking you, little one," All For One praised. "I have been longing to reclaim my younger brother's keepsake for many, many years now. Thanks to you, it's finally back where it belongs."

"That ruby has been on my family's trident for generations…" Izuku muttered aloud. "You would have to be hundreds…thousands of years old—"

"Yes?" All For One said, lips quirked in amusement. "I am much older than my appearance would suggest. I was there when the mers first arrived in our waters and fought in the wars that followed. I was there when the mers hunted us to near extinction."

"I…mers tried to…to exterminate the Cecaelia?" Izuku repeated weakly.

"The key word being tried," All For One said lightly, as though merely discussing the flow of the currents. "We were stronger but they had numbers on their side. They were fearful of our power and sought it for themselves. Once they had it, they no longer had a need to keep us around." His voice suddenly darkened, eyes flickering back to the necklace he wore and the ruby that now adorned it. "My younger brother…he…" All For One trailed off, and Izuku watched as he turned his head away briefly. But not fast enough that Izuku missed how he blinked his eyes several times. "Anyway. There's still a few of us left, scattered across the ocean. We mostly keep to ourselves these days, but every century or so I might run into another of my kind. It's rare that we show ourselves freely. For obvious reasons."

"Oh…I'm…I'm so sorry…" Izuku muttered, tail curling and fins drooping. His heart ached for the Cecaelia. He had no idea what it must be like to live through that kind of trauma.

"But that is a tale for another time," All For One mused, reaching a hand out and carding his fingers through Izuku's curls with a chuckle. "You should be happy, little one. You've completed your end of the bargain, and now I will fulfill mine. This is a momentous occasion!"

"I. Um. I had a…question, about the things you had me bring you," Izuku spoke nervously. "They…I mean you…" Izuku started, cursing himself for his own stammering, his embarrassment only further worsening when he saw All For One's amused smile. "I-I've been wanting to clarify something," Izuku finally managed. "…You didn't really need any of those things, did you?" Because Izuku had been trying to puzzle out what kind of potion would use that list of ingredients ever since he'd first been given it. And he'd drawn a blank. He could understand why All For One would need one of his old belongings but not the crown in particular. The golden algae was too toxic. A human's tear seemed completely nonsensical in a ritual to transfer power between a mer and a Cecaelia. And Izuku was fairly certain All For One had only wanted the ruby because it belonged to his brother, no matter his claims.

The smile on All For One's face only grew, seeming impressed by Izuku's deduction.

"It is as you say, guppy," All For One confirmed with a single nod. "I already had everything I needed to begin with."

Izuku's confusion deepened, only able to stare at the Cecaelia for several long seconds before he found his voice again. "B-But why? Why have me obtain so many rare items if you didn't actually need them?"

"To test your strength of will and determination; to see how far you were willing to go to achieve your goals," All For One answered simply. "The act of gifting magic is a strenuous one, and not something to be given away lightly. You would not give away something of incredible value to someone who hadn't proven themself worthy of such a thing, would you?" At Izuku's slow shake of his head, he continued on. "I had to ensure that you really were deserving of such a gift. And if I had simply given it to you from the beginning, you might never have learned how clever or resourceful you could be."

Izuku wasn't quite sure what to think, but a part of him saw the logic in the Cecaelia's words and the purpose of the tasks that had been set out for him. Still, he couldn't help but feel a touch of doubt. He could have died carrying out those tasks! All For One seemed to notice, his voice softening.

"Izuku, do you know how many people have come to me, asking for things beyond their capabilities?" He spoke gently. "Do you know how many of them were willing to go the lengths that you have gone to to achieve your goal?" He grasped Izuku's chin, tilting his head up from where Izuku had turned his gaze to the sandy floor so that green met red. "Very, very few, little one. You had the drive and the competency to reach out and take hold of what you wanted. And all without magic! Do you know how impressive that is? How incredible you are?"

Emotion choked Izuku's throat, a sniffle escaping him at the Cecaelia's praise, and he found himself unable to see as tears blurred his vision. He brushed at them futilely, sobs threatening to escape him when he felt a hand squeeze his shoulder in a comforting gesture, patiently waiting for him to calm.

"And now I will fulfill my end of the deal," All For One said once Izuku managed to beat back the tears. The Cecaelia moved around his cave, pulling out some very strange objects: a pillow and two blankets.

Izuku blinked. "Those are ritual ingredients?" His mind flashed through a thousand books but he could not figure out what the pillow would be used for.

All For One chuckled. "No, I'm making a place for you to lie down." He put the heavier, gray blanket on the cave floor, using pins in each corner to stop it from floating off. Then he added the pillow and second blanket. "The ritual will be exhausting for you." Several of his tentacles moved rapidly as he drew a circular pattern on the ground, around the blanket.

"Oh, thank you." Izuku sat down with his tail curled up. All For One puttered around his workbench, mixing together ingredients into a jar. He poured the mixture around the circle, where the particles stuck to the lines on the ground and glowed. Izuku spotted jellyfish fronds and octopus suckers, ingredients typically used in transformation spells. That made sense, given that All For One would be transferring magic to him. Though Izuku himself would have achieved that with a ritual to open up a channel between them. He assumed the ancient Cecaelia knew what he was doing. It was probably a lot harder to transfer magic.

All For One bit his own tentacle. Izuku gasped. The Cecaelia held out his bleeding tentacle over the circle, and the drops seemed to magnetically flow down the glowing lines.

"You're losing a lot of blood," Izuku said nervously. "Are you sure you need that much?" He made an aborted gesture to rise, then stopped. He knew better than to disturb a magical ritual in-progress.

"Don't worry, our kind heals quickly," All For One said absent-mindedly. "See?" He held up his tentacle, the cut already faded to a barely visible white line. "Now, it's time to begin." The Cecaelia gestured for him to lie back.

Izuku tried, but curiosity got the better of him and he sat up again. All For One glowed with power, from his eyes to the suckers on his tentacles. The water swirled around him, humming. Mist rose up from the circle. Izuku's entire body tingled as it touched him. His eyes felt heavy. He yawned.

"Rest, little one," All For One murmured. He held out a rare sea turtle shell and crushed it between his fingers.

Sea turtles, being long-lived creatures, were used for de-aging magic. To destroy the ingredient represented a sacrifice, the destruction of the recipient's years of life. This was not a magic transfer ritual.

"What are you doing?" Izuku screamed, betrayal and fear swirling through his heart. He leapt up, trying to escape the ritual circle no matter the consequences. But the blanket leapt up and pinned him down, transforming into a stronger material. His limbs would barely move, the pins and needles sensation spreading all over. A splitting pain came from his tail, as if it was being wrenched into pieces. His arms had turned blurry, but Izuku thought his hands looked smaller. The glowing light covering his body made his eyes burn. Tears fell, partly from the physical and partly the emotional pain. He'd thought he'd found a friend, someone who finally believed in him. In his joy he'd overlooked his nagging doubts. As he fought, Izuku's gaze sought out All For One's, desperate for an explanation.

The Cecaelia smiled, a triumphant expression. "You don't need to be scared. I won't hurt you. I changed my mind about that. Just go to sleep."

"Why?" Izuku pleaded. His lips could only manage one word before the numbness took over. He fell backward, collapsing into the blanket. The blanket…had definitely gotten bigger…or he had gotten smaller…

Toshinori had run to the throne room as soon as he'd woken up. Without even gathering his warriors, he'd leapt through the portal in the mirror. The magic could track his son's location, as a member of the royal blood.

Toshinori came out inside a dark cave. There was no sign of his son. All For One sat in a blanket nest, humming a song. There was a smile on his face, and a soft chuckle echoed throughout the den. That smile fell at the sight of bubbles floating upward. He looked up, irritation crossing his features when he took notice of Toshinori. There was a spot of algae growing in his otherwise pure white hair.

The sight would have been comical under any other circumstances. But Toshinori's nerves had been stretched to the breaking point. He growled, "Tell me where my son is before I kill you."

"That's not a very good bargain, you buffoon. You're bad at this." All For One rolled his eyes.

Rage filling him, Toshinori advanced. Even without his trident he would rip the Cecaelia in two. His warriors should be following soon, he'd screamed at his attending doctor to gather everyone in the castle. But he could not wait.

A very tiny baby, no longer than a finger, leapt out of All For One's hair and floated between them. Snarling, he released a cloud of ink at Toshinori.

"You don't need to defend your own father, little fry," All For One murmured with astonishing gentleness, cupping the baby and pulling him away.

Toshinori could not move, even as the ink struck him in the chest and neck. He stared, transfixed. His arms hung slack. The baby Cecaelia had eight green tentacles to match his green hair and eyes. That look of rage was completely familiar. Toshinori had seen it on his son's face. "Izuku…son…"

"My son, now," All For One said cheerfully. "He doesn't even remember you. Do you, baby?" He cooed at the fry, who giggled, seeming to respond to the tone rather than understand the words. "If you cared about your son, then you should have looked after him better. Poor Izuku felt so neglected that he came to me, seeking magic. At first I sent him on a silly wild goose chase across the ocean, hoping he would die and you would lose your entire family just like me. Even if he had succeeded, I would have transformed him into one of my Nomu guarding my cave. But…I have to admit, that child is remarkable. He's far too clever and talented for a buffoon father like you. I finally found someone worthy of replacing my little brother. Since your family destroyed mine, I think it's only fitting that you provide me with a replacement."

Those words finally shook Toshinori out of his shock. Fury filled him at Izuku being called a replacement. He lunged, magic swelling up his arm.

All For One laughed in his face and vanished. The transformed baby Izuku vanished with him.

Then the corrupted mer broke through the doorway and attacked.

All For One floated along the ocean floor, soothing the crying baby clinging to his hair. "Yes, I know that hideous man was dreadful and scary. I would have killed him, but I couldn't risk you getting caught up in the fighting. Perhaps someday when you're grown, we'll kill the blond buffoon together." He chuckled darkly. One tentacle very gently petted the tiny fry's hair. "It's a shame to leave behind my cave, but I have many others. I left plenty of traps behind for the foolish mer invaders. My Nomu will distract the blond buffoon and his people long enough for me to craft a spell to hide your magical presence and prevent them from tracking us. I have a nice, safe cave deeper in the ocean, suited for raising a child."

The baby Cecaelia yawned and snuggled down in his hair.

"Yes, you should rest." All For One smiled upon hearing the tiny snores of his new child. "I'll look after you, my son."

OMAKE TIME!

Omake: A Biased Story

Izuku: Your brother's death wasn't your fault.

All For One: You're kind to say that, but I failed to seal him inside the cave well enough and he swam off.

Izuku: …It sounds like it might have been somewhat your fault, actually.

#

Omake: If Only Aoyama Could Talk

Izuku: All For One gave me a token to ward off Nomu. How generous of him to part with a treasure.

Aoyama: I think he just ordered them to leave you alone. It's rather telling that he didn't do that to begin with but he was planning to get you killed.

Izuku: I heard All For One drained his power to help you obtain magic, what a noble soul.

Aoyama: It took him five seconds and he had plenty of magic to throw me out of the cave right afterward.

#

Omake: Open to Interpretation

Inko: Did you kill me in the end or not?

All For One: Who knows? Maybe your husband was too paranoid, maybe it was all a subtle plot. But look at it this way: you died so that your son could get a better parent.

Inko: Someone get my frying pan, I have a potato to mash.

#The true history of mer and Cecaelia is also open to interpretation #I would not unconditionally trust All For One's version #But the mer were far from innocent #Both sides were trying to wipe each other out

#

Omake: Trading Down

Izuku: My father is too overprotective.

Yoichi: Boy did you ever make a big mistake trading a reasonably overprotective dad for All For One. You'll find out in a couple decades.

Author's Note: Happy Mer May! Delete the spaces to get the link to some cool fanart of Mer Izuku by thebnha-auhoard:
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thebnha-auhoard/723043848784314368/new-session-archive-of

In addition, In addition, transfemdeku drew our adorable baby Izuku with his new "father." Delete the spaces:
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transfemdeku/730704528427663360/fanart-for-sinking-into-the-depths-hey-all-might