Killua figures out fairly quickly he's a complete failure of a Zoldyck.

After watching his two brothers go through it and all the embarrassing "you're maturing" speeches from his family, Killua had thought he was reasonably prepared and knew what he was up against. Frenzies, cravings for humans, lack of control, mood swings…the whole nine knots, but he hasn't felt any different. If anything, he's felt more empty. He can barely summon the desire to float around the garden and rarely eats anymore. He hoped in the first difficult weeks the taste would eventually grow on him like some kind of parasite, take care of the disgust that rises in his gut with every meal, but now, a month later, he prays he's a late bloomer. There's no way he can on the edge of starvation for the rest of his life.

Even with Alluka managing to sneak him food more often than not (a few scraps of fish or what have you), Killua hasn't felt full since coming of age. Sometimes he has to choke down a human just to stay alive, barley able to even swim into active waters with how weak hunger's made him.

The worst part is he doesn't know what his problem is, so he can't even begin to try and fix it. Humans smell delicious, sure, and his mouth still waters at the idea of tearing into something with that kind of scent. But when it comes to actually eating them, every bite is like wilted seaweed in his mouth no matter the kind of the human.

Grandpa Zeno's notably worried, which sets the whole family on edge. Killua's actually been asked— albeit in a roundabout way— if he's feeling okay, but his grandfather seems to assume it'll pass. At least he decides it's nothing severe enough to deter training Killua from taking over the family.

The new, more academic training brings surprising relief. Finally, something he can do right. Killua's proud to say he knows all of the human alphabet and how to spell his name after only a couple lessons and tries not to think about how he's supposed to eventually use this knowledge to "help his family." He's even been able to sound out a few words he's seen at the beach, names of stores and such that he can see from his perch out in the ocean. Sometimes a small group of humans that smell really weird will march up and down the beach, shouting about "cleaning water" and "saving fish" or whatever, but Killua can figure out most of the words on their signs by sounding them out.

He thinks it's kinda funny that one of them gets this really shrill voice when another humans challenge her just like his mom does when she goes on one of her tirades. Same lecturing tone and everything!

...

Maybe that's it. Maybe if Killua stopped going to see the humans, stopped seeing them as equals, he wouldn't feel so nauseated every time he had to eat one, but it's…he can't do that! Not now. Not after spending the last two months spending his days listening to the waves crash and the people live.

Say what you want about their stupidity and violence, but humans are fascinating to watch. Like why do they go swimming when they know (almost) all the dangers that would love to eat them? Why are they so instant on having colorful cloth cover their bodies at all times? Why does it take them so long to eat one thing? Why do some of them wake up so early to see the sunrise if it'll make them cranky later? Why is jumping oddly around a campfire in a "dance" so much fun? Why do they laugh so loudly when "it" catches them? Why do they always seem so damn happy?

(Why does Gon come back every day just to dangle a hook in the water when fish rarely wander in this far? Why wasn't he there the first eight days Killua started visiting the beach? Why does that dark haired girl from before always bring him food? Why does he wear the same bright green shorts every day? Why is his hair always so pointy? Why does he always look so happy even when he never gets a bite?)

Killua spent his whole life waiting to ascend to the surface. Now that he's done it, he has no idea what to do with himself. The very act of eating is becoming a chore, and with the duty of ruling over his family for the rest of his life stretched out inevitably before him, going to the beach feels more and more like a necessity. It's the only escape he has left.

And yet the more he sees the human's daily life, the deeper jealousy claws his chest.

And when the questions are overwhelming him it's not like he can just swim up and ask them why "dancing" is different from "spinning" but Neptune would he like to know. If there were anyway he could just talk to one of them for a minute or two, sate at least some of his curiosity, he'd take it in a heartbeat.

Apparently his growing desperation on top of his failing health is enough to worry even Illumi, who shows his worry through his standard lecture—humans are food, Zoldycks evolutionary miracle, blah, kings of the sea, blah, blah— and for once in Killua's life, it actually helps.

See, his brother was heading out to see the sea witch, Hisoka, when he stopped Killua.

Sea witches are an immensely powerful creatures, ones even the Zoldycks wouldn't like to get on the bad side of. They can do the impossible—be the impossible— and sure, Killua can't approach the humans as a Zoldyck. But as a human himself? No one would be the wiser. His family wouldn't suspect a thing if he was gone for just a day or two. A few days to eat something besides leftover fish, like that chocolate thing he's heard of, or maybe some potatoes. Enough time to get some answers. Maybe he could talk to Gon.

Of course there's no way in hell he's going to Hisoka. He'd tell Illumi exactly where Killua went after reaping the benefits of a cockeyed deal.

The sea witch down south, however…

"Hey~? …Hello~?"

Killua's voice tumbles uselessly into the black abyss before him, not even bothering to echo back before it dies.

"You there~? I wanna make a deal~!"

Nothing.

He sighs, drawing away from the vastness before him. The witch is supposed to live in this trench, but he's beginning to doubt his information. How can she stand it? Just looking into it makes Killua feel tiny and frail. If she thinks he's going down there without some kind of light, she has another thing coming.

"Hey! Old ha—"

Killua's sharply cut off as he's jerked down into sudden blindness.

Gasping in pain, he slaps his tail as hard as he can against the invisible thing crushing his waist in the darkness. A jolt of panic shocks through his body when it holds tighter, constricting in a way that makes the long-forgotten feeling of fear hammer in his chest. Zoldyck tails are one of the strongest things in the sea. If this witch—at least he hopes it's the witch—can keep her grip on him…

Hard rocks cut into Killua's back as he's abruptly slammed onto the sea floor, and the impact rattles in his head long after the grip on him loosens. Whatever it is that grabbed him lingers over him in a silent threat before retreating entirely out of sight, which only makes his situation worse. At least he could keep track of it when was pulling him. Now it could be anywhere.

The bottom of the trench is odd. A wide circle of artificial light comes from a large crater in the center and encompasses the area around Killua. He's surrounded by strange cages and bottles of varying size and color the drift lazily around him, a few human nick-knacks in the mix as well. It's nothing impressive, but the water around Killua feels heavy with power and hard to breath, and the whole layout unsettles something in the Zoldyck. The trench feels like it's for show, somewhere to be occupied rather than lived in; an elaborate stage crafted just right to feel wrong.

A small girl lingers right on the edge of the ring of light, her hair pulled into tight pigtails by vibrant ribbons that twist like writhing snakes in the water. She must be the sea witch, Biscuit Krueger.

Killua rights himself and sizes her up. She looks so…young. No older than Alluka at least. Her appearance deceptively normal too. She could be any old mermaid from the seas a little farther west of here with her short stature and bright tail, but witches typically aren't mermaids. In fact they tend to be half-breeds or mutants of some kind. Is that why she's hiding down in a hole?

"What was that you called me?" Her sickly sweet tone makes Killua cringe with its razor sharp edge just as much as the silhouette of a tentacle shifting threateningly behind her.

"N-nothing!"

So not a mermaid then.

The cute face that beams back at him does little to reassure him. "That's what I thought." Biscuit takes her place in front of her fissure, her face framed menacingly by the light. Killua doesn't doubt she did that on purpose. Hisoka can be pretty melodramatic too. Must just be a witch thing. "So how can I help you? You want vengeance? Beauty?" Her eyes twinkle as she grabs a particularly foreboding bottle drifting by. "Love?"

Killua shifts back as far as he can from the sea witch while remaining inside the light. "Um…none of the above? I need legs." He flicks his tail nervously before clarifying, "I want to be human. For a day or two! Not long."

Much to his surprise, Biscuit just clicks her tongue in annoyance as she turns to her bottles. Killua kinda feels a little insulted at her sudden lack of interest. "Can you afford this kind of magic, kid? This is powerful stuff in its own right, but a spell that works on a Zoldyck, let alone one that turns them human? That's in a level all its own." Biscuit peers back at him. "Some say it doesn't exist." She shrugs. "I say some just don't have the intelligence to imagine such power."

"So you can do it?"

Biscuit chuckles at Killua's hopeful expression. "I told you that's not the problem. The issue is the expense—is that what I think it is?!"

There, sitting in Killua's palm, is one of the most valuable gems in the world, Blue Planet. It's been unseen for more than a decade, but there it is, shinning clearly even at the bottom of the trench in all its legendary glory. The witch drools as she watches in the inside of the gem swirl like an invisible whirlpool, forever imitating like the clouds in the atmosphere just like the stories say. Biscuit's hand unconsciously drifts forward.

Killua closes his hand, hiding it from view. "So you can do it?"

Biscuit snaps out of it and darts towards her bottles, grabbing five in her hand and dumping them into her fissure to turn the light an icy blue. "It'll be done in just a minute!" She tosses ingredients into her concoction haphazardly, barely pausing to check what she's grabbing before pouring it in. Sometimes she even throws in the whole bottle.

Killua watches the trench's mixture shift into dizzying colors with a sense of growing dread. When it finally settles into a muddy brown that reminds him of ocean scum, he can't help but ask, "So what exactly is this potion gonna do to me?"

Biscuit barely spares him a glance, uncorking a purple bottle to sniff its contents. She makes a disgusted face before tossing it in. "Well, you do know there are some major differences between your body and a human's despite how similar you look, right? This potion's going to rearrange your organs and grow you all the parts of a human you need."

Oh, is that all.

"You're going to be sore for a long while after the initial kick, and there may be a side-effect or two since you're so young," Biscuit shrugs nonchalantly, "but I'm not some bottom-feeding barnacle. All terms and conditions will be explained to you, and I'll do my best to get you to land without dying once you drink the potion."

"I can't just take it near shore and drink it?"

Killua hardly thinks his question deserves such a strong snort of amusement from the sea witch. "Are you kidding? Kid, how many creatures do you think would love to rip you apart once you're completely defenseless? And you will be defenseless. No more indestructible skin. No more sharp teeth or claws. No more breathing underwater for more than a minute. Hell, you won't even be able to swim because of one of the one of the side-effects. Defenseless." She stops long enough to raise as eyebrow. "Plus I assume you want to be secretive about this. I don't think your old man would be happy to hear about our little deal."

Well…yeah.

"On top of that, you're going to be really incapacitated. Unless you find a way to covertly get on the beach and drink this without drawing the attention of any humans, you're going to drown if you take this alone because there's no way you'll be able to swim to shore when the convulsions start. I can take you if you drink it here, though."

Biscuit seems to take his lack of visible fear as a challenge because she gets progressively more dramatic as she brews, even going as far as to throw a whole, star-shaped bottle into the fissure and stand in the resulting discharge. Killua has to hold back a snicker when she chokes in the orange swirls.

There's only a few more doses of this and that once Biscuit recovers, successfully finishing the potion and killing the small good mood that had settled in Killua. She easily captures the concoction into a triangular container and comes to stand in front of the Zoldyck. Killua's stomach turns. It's still the color mud.

"Okay! Quick, simplified explanation." Biscuit taps her jaw. "You'll be growing various parts in a very, very painful manner. This isn't a cakewalk. For example, you need to grow vocal chords as well as legs. It hurts at first, you're sore for a day or two, and you're good. You'll have one set of teeth as a human, so don't be surprised when that other, sharp Zoldyck set you have falls out." Biscuit ticks each subject off on her fingers as she talks. "You're gills will be smoothed over by skin, your skin will become squishy, and taste for blood will be suppressed…mostly. Don't try eat anyone, got it?"

Biscuit sighs and shakes the bottle. "I don't know why, but that and smelling things just never go as planned. The feet got some kinks in them too." She nods thoughtfully. "You know, not a lot of fish want to be human, especially after learning how painful it is to take the potion, but the ones who come back tell me every step is like walking on swords. You can trade something to dull the pain…perhaps your voice?"

Killua barely manages to hold in a snort at the expectant witch. Is she kidding? How is he supposed to find out stuff if he can't even ask questions? And what are a couple of feet cramps next to the things he's already endured? Biscuit's seriously underestimated how far the Zoldycks are willing to toughen up to keep from going extinct. They're born pretty indestructible to begin with, but there are plenty of other things they have to build immunity to from day one. Can't have a curious young one die because they brushed up against the wrong type of fish while playing.

"I'm good, thanks." He accepts the bottle with mixed feelings and tries not to flinch at how hot it feels in his hand. It's impossible to tell whether it's fear or excitement jittering in his stomach now. "So… how much do I take? When does this wear off?

"It doesn't."

Killua blinks. "Then how am I supposed to get back?" he asks flatly,

Biscuit clasps her hands together. "Well that's just it. My potions have a bit of a built-in clause. There'd be no way to get this kind of power without a deal, you know? So, you got a year- maybe a year in a half for you since you're not full-grown- until it wears off. If, by the end of your time, you have not returned, you will become sea foam. And die. Sorry 'bout that." She really doesn't look that sorry. "That gives you two options: either become fully human, or drink another potion I'll have to whip up for you."

Killua regards her suspiciously. "What kind of potion? Why don't you give it to me now?"

Biscuit waves her hand, brushing his concern aside easy. "The price is different for everyone. The next potion will have to compete with your attachment to the surface and its humans. Better to hurry back, understand? Don't get too attached to some prince like my last customer.

"Now," Biscuit grabs a glowing stone slab and a shattered piece of a shell floating by, "this claims that you fully understand all risks and I am in no way responsible for your fate up on the shore. If you die before you reach the surface, this contract will insure I'll die as well. Customer confidentiality, blah blah, I hold the right to check up on you at any time boring, boring…I will appear when you call and wish to return so I can assess the damage, yatta…got it?"

The bottle is hot in Killua's hand. Hesitation sits heavy in his chest and only grows as the seconds pass. If he doesn't do this now, he's going to back out. He steels himself and acts.

In one fluid motion Killua signs his name, drops the gem into Biscuit's stunned hand, and downs the potion in one gulp, holding back his gag reflex as it slides down his throat.

"Don't drink it yet! I'm not ready!"

Well too late now.

His gut lurches in what he assumes is nausea from the nasty taste left in his mouth, but then it rolls again. And again. Pain builds until he can't even hold the empty bottle in his numb fingers.

Biscuit curses, drops the gem. She rushes to his side and yells…something. Killua can't hear passed the surging in his ears, can barely feel her wrapping him in an awkward hug, can't even see the angry hysteria in her eyes.

Dimly he's aware of the light growing brighter, the pressure wrapped firmly around his middle, the sea rushing passed his body, but they seem so insignificant. He's weak and shaking, barely a moment's rest before the next wave starts and ends and starts and ends and starts until it doesn't even stop anymore.

There's throbbing in his tail. His tail. It's not supposed to do that. Tails don't hurt.

Something glints in front of his eyes. One of his scales?

A knife stabs through Killua's neck leaving him gasping, water rushing in to his throat the wrong way, surging into his nose, and he gropes blindly at his neck to pull the knife out but he can't find anything. Not even the slits of his gills, and he can't figure out how to breath anymore, why won't his gills work, why is his tail so painful—

Panic slams into Killua, dulling the pain for the brief moment is takes him to process exactly what's happening, to understand he's drowning.

For a hysterical moment he thinks it's hilarious. A Zoldyck is drowning. The deadliest predator in the sea is drowning.

And then blind instinct kicks in. He starts thrashing, clawing at the pressure around his waist, fighting to swim what he hopes is up towards the surface, but he thinks they pull him down, farther into the sea to drown and he knew he should of told Alluka where he was going.

Relief comes in cold air smacking his face and a deep, heaving breath that frankly hurts about as much as it helps. His head spins, light and empty and he thinks he sees stars, but there are no stars underwater.

Weakly he tries to move his tail, tries to figure out how much damage is done, but the wave of pain that blasts through his body is just too much.

Killua passes out.