Izuku skidded to halt, panting as the glow around him sparked and dimmed. His head throbbed, but that wasn't his main concern. The cold in this cave was his biggest issue. He couldn't have been tied up for long, but the lack of movement brought him too close to hypothermia for comfort. Thankfully the energy from One For All heated his body just enough to abate the effects, but he needed to keep moving to ensure he brought his body back to safe levels.

The glow around him faded entirely, plunging him into total darkness. He took a few more seconds to catch his breath before sparking his Quirk. The cyan colored energy flickered to life as small bursts ran across his body, just barely lighting up his surroundings. It was all he had once realizing most of his stuff was gone. Whoever knocked him out had left him only with his hero gear, which was strange enough.

Not so much as a guard to keep watch, Izuku thought as he got moving into a brisk jog. They could have just killed me. So why not? They want me for something. To toy with me? But why? What purpose would that serve?

He spotted a side tunnel and he hesitated. The way forward was obscured in darkness, and this passage was no different looking. He stepped up to it and lowered his scarf, trying to feel for any hint of a breeze. He grimaced after feeling nothing and lifted his scarf. He raised his boot and slammed it down, creating a small crater in front of the tunnel before moving on. That made the third side tunnel in the last ten minutes. He couldn't be sure any of them would lead him out, so he kept going forward with the hope that it wasn't leading him further in. There was always the chance one of those three tunnels was the way out and that he was just too far in to feel any wind. Yet it was going to be a risk he'd have to take eventually if this way led to nowhere.

A flash of pain shot through his skull and he whirled around, nearly slipping on the icy rock as he came to an abrupt halt. The sensation was familiar. It was a warning. "Who's there!?" He shouted as he amped up One For All's output to 20%. The energy glowed just a bit brighter, providing more glow, but the darkness still permeated beyond its edges. He could feel the throb in his head, different from the pain. He twisted his body around until it felt like something clicked in his head. That's where the danger was located.

Danger sense… Izuku blinked. That thought hadn't felt entirely his. He shook his head and raised both fists. "Whoever's there, show yourself!"

Cold laughter echoed around him and his danger sense flared at the same time his heart almost stopped from the sound. He instinctively threw himself sideways just as a chunk of rock emerged from the shadows and shattered against the wall behind him. Spinning himself on the ground, Izuku used his momentum and kicked himself in the direction the boulder came from. He swung his leg, a burst of wind sailing into the darkness. He heard it crack against rock and he stopped his leap just before he hit a wall. He spun around, but there was no one, and the feeling of danger quickly faded.

He raised his hand and gripped the front of his costume. His eyes wide and his breaths coming in short gasps, he swallowed thickly. That laughter- He shook his head and forced his hands to stop shaking the moment he realized they were. Whoever was in here with him was definitely toying with him.

He began running, his senses on high alert. He couldn't afford to stay here. He had to get back outside. Whatever aspect of One For All was allowing him to sense danger was a blessing, but it would likely only go so far.

I sure hope you're having a better time than me, Set.

"Get him in here!" Setsuna ordered as she forced herself to remain calm. Jurota hurried after her into the small conference room and laid Izuku down on the table. Itsuka and Ibara were close behind Setsuna as they carried a first aid supply.

They'd only just gotten an unconscious Yamatora out of the basement and into this same room when Izuku's group returned with the teen in question also unconscious and bandages wrapped around his head. The entire squad looked beaten and half frozen to death.

"You two got this?" Itsuka asked both girls, and when they nodded, Itsuka turned back towards the door. "I'll be with the sick. They're… not good."

"Itsu," Setsuna stopped her by grabbing her arm. "The fear, are you-?"

"As good as I can be," Itsuka interrupted her, giving her a forced smile. "Can't afford to let it get me down, we have poisoned citizens to worry about."

Setsuna nodded and let her go before turning her attention back on Izuku. Ibara was already at work, peeling back the bandages around his head. She made a face. "He probably has a concussion." Her vines were shifting through the first aid bag. "How long has he been unconscious?"

"Not very long," Jurota answered as Ibara began to dress the head wound. "But he's been unconscious at least once since we were ambushed the first time."

"First time?" Setsuna narrowed her eyes. "What happened out there?"

"I can give you the full rundown of the situation gone awry," Reiko spoke up from the doorway.

Setsuna glanced at Ibara. "Will he be okay?"

"Yes," She said with assurance. "It's not that bad. Go, Jurota and I can take care of him."

Nodding, Setsuna motioned for Reiko to lead the way. They moved to a quiet corner in a hallway not too far away. Reiko looked haggard, and her costume had several tears in it and a small cut seemed to have stopped bleeding on her cheek.

"We had made our way to the store to retrieve the charcoal medicine," Reiko began. "I suspected we were being followed, and when we were in the store, Izuku and Kohaku stood watch. Izuku was ambushed and Kohaku was taken by the villain. With no way of knowing where they were, and Izuku being injured, we… I…"

"It's okay," Setsuna gripped her shoulder. "Given this whole situation, there wasn't much we could do. We'll rescue Kohaku, and we'll stop these villains."

Reiko pursed her lips, but nodded. "With the evening setting in and darkness along with the blizzard, we had to return here. On the way we discovered that much of the way back had been leveled, perhaps from the earthquake. Not two streets away we were attacked by an ice villain, quite possibly our murder suspect. We were only just able to fend her off before returning here."

"They're toying with us," Setsuna muttered as she gripped the wall. "They definitely have the advantage. They've attacked us several times, murdered innocents, and poisoned the water. What are they planning!?"

"Set-" Reiko hesitated and Setsuna glanced up at her. "There is perhaps one more issue we need to consider."

"This cannot be the way out."

Izuku stood near the edge of the ground overlooking a yawning abyss, the sparks from One For All unable to penetrate its depths. He raised his gaze, unable to see if there was another area he could reach. He tried stepping closer to the edge, focusing all his senses on falling. Other than a sense of dread, he didn't feel any danger.

Maybe it can't detect if I'm about to put myself in danger, Izuku theorized as the gears turned in his head. Can it only sense danger being done towards me? But wouldn't this still count? Unless… It might have to be from someone, or even something, actively out to get me. Does it read their emotions? Sense that they're putting me… in danger… Wait!

He turned on the spot, cold and potential danger lurking in the shadows momentarily forgotten as a memory came back to him. Before he'd even started having dreams of the past vestiges of One For All, he, Setsuna, and Neito had spent much of last winter break researching them. They hadn't been able to find much about the first few users, not even their Quirks, but there were a few Sir Nighteye had looked into. Toshinori Yagi, aka All Might, was easy, since Nighteye knew practically everything about him, including that he was originally Quirkless. It was through him that he also knew a lot about Nana Shimura, the user prior to All Might. However, there was hardly anything concerning the one she got One For All from, aside from the codename: Amaterasu.

The Fifth was actually much easier because he made a big name for himself as Lariat, his Quirk Blackwhip being one of Izuku's favorites to theorize on how it could be properly implemented as a defensive, support, and offensive Quirk.

Needless to say, none of those were the ones Izuku thought about. Because it was the one report they'd managed to dredge up from old internet forums concerning the Fourth User, and his Quirk, which no information was given except for its name: Danger Sense.

Danger Sense. The moment he thought it, it sounded right, as if something clicked into place in his brain. He, Setsuna, and Neito of course bounced their theories on how it functioned off of one another, but now… If this is Danger Sense, then the question I need to ask myself is how I have it. Izuku shook his head. One For All. Somehow, someway, One For All has given me Danger Sense. Perhaps-

His mind, no, Danger Sense flared just before the ground began to shake. Izuku didn't have a choice, taking a leap into the darkness just as the ground he'd been standing upon exploded. He became enveloped by emptiness surrounded by darkness, unable to see where he was going as he soared. A second later he saw the opposite wall along with an opening. He created an air burst with his fingers, directing himself towards it. As he landed, he heard the rubble behind him hit the ground. It was a long drop from the sound of it.

He also heard a sort of grunting and sniffing sound before he heard the further destruction of rock, which slowly faded away. Izuku felt even more uneasy now as he began running. He'd suspected a mole-mutation Quirk of sorts, and while he didn't see his assailant, he had a strong suspicion he was right on the money.

Just as he passed the opening to another tunnel, Danger Sense rang louder than before, and Izuku didn't even have time before he was slammed sideways. He tumbled along the ground, wincing at the pain. Danger Sense hadn't faded and he glanced up just as he heard something heavy moving through the still air. He saw metal and sharp edges before he threw himself away. The weapon slammed into the ground, spraying chunks of rock. One of them tumbled by, half melted from some sort of corrosion.

"Heh." The sound made Izuku shudder. "You have excellent instincts and reaction time. But you're not quite perfect, not yet. Tell me, Izuku Midoriya, one who follows the path of All Might, are you able to do what it takes to beat me?"

"Who are you!?" Izuku demanded as he stood, trying to make out the villain. He couldn't see anything, only hear him, and he wasn't willing to move any closer. The villain had no source of light, which meant that he possibly had a Quirk that allowed him to find his way around in complete darkness, or he'd been in these caves long enough to know them by heart. Either option was bad news.

There was complete silence for a few moments before he heard raucous laughter. "Oh, this is too good! You don't remember me? Heh, pity. But I remember you." He heard the villain begin to approach, something heavy and sharp being dragged along the ground with them. "Let's see if we can't jog that memory of yours."

Izuku had two options. Stay and fight, and learn who this villain was, or run. The option was clear to him. He swung both hands together, mentally shouting, FLORIDA SMASH! The resulting boom rattled the cave and rained down debris. He heard the villain grunt and the sound of him skidding backwards, but before he could react, Izuku was already running in the opposite direction. He didn't stand a chance down here with limited visibility, not when the opposition clearly held the advantage. Learning who he was could come later, but now that he knew he knew them, his voice did sound familiar. But why couldn't he remember-!?

Izuku suddenly felt a breeze hit his face and he poured on the speed. He found himself back in open air as he plowed through a heavy bank of snow. He came to a stop, no longer surrounded by rock, but snow. The wind chill was biting at his face and he could just make out a few trees around him on a downward slope. He must be somewhere on the mountain, but he couldn't make out much more than that in the ongoing blizzard.

When he took a few cautious steps forward, his foot sank into the snow and hit something hard. He blinked and suddenly he was no longer in a blizzard surrounded by snow. He was on a rooftop in the dead of night. There a helicopter sat, ready for takeoff as the blades whirled. The wind blew in his face as he watched an unconscious Setsuna being hauled into a helicopter by a hulking figure.

"Setsuna!" He yelled, about to race forward.

"Don't even try," the villain raised his hand. In it sat a device. "You are an annoyance, Izuku Midoriya. So desperate to live up your ideals. You even gave Setsuna ideas of her own. That's no good. So let me destroy those for you. You wanted to save everyone, right? So let's see if you're really up to the task." He pressed down and several explosions rang out below in the skyscraper. Izuku felt the roof shake and suddenly he was faced with a decision.

"Come and save her," The villain said with a laugh as he climbed into the helicopter. "I have no doubt you could. But can you really waste precious time while this building's supports fail?"

Izuku wasn't here. He couldn't really be here. This was just a memory of his first year at UA. The villain, Rectifier, was someone he'd already beaten. All of this already happened.

Yet he could feel the building's supports begin to fail as the helicopter began to lift off the roof. He saw Setsuna's limp form in the seat and his heart ached. Despite knowing all this couldn't be real, he longed to save her. But he could only make the same decision as before.

Pushing One For All past its limits, he turned his back on her and raced into the building. He had to save everyone before the building collapsed. But the outcome was already certain. He would save only a few, the rest consumed by the debris. There would be few survivors from that. He'd failed to save everyone.

All Might could have done it. With the full power of One For All, he could've saved everyone in a heartbeat.

This was one of the defining moments of Izuku's life. The moment he truly came to realize the weight of being a hero. Sometimes he'd be forced to choose between the one and the many. And even then, he'd still fail to save everyone.

He found himself surrounded by fire again. He wanted to cry. He was back here on the day his whole world was destroyed. The moment his childhood ceased to exist and he was thrust into the full cruelness that the world could offer. The day he saw his hero fall.

But like before, it didn't quite play out like he remembered. All Might fell, his blood coating the ground, but the villain stood over him, laughing in triumph. A laugh that filled him with unfathomable horror.

"This is wrong." The words fell from his lips as he shook upon the ground. "You're-He defeated you-!"

He remembered All Might taking the villain's weapon, breaking it in half even as the substance coating it ate at his hands. Even as he took a blow to his stomach that had sprayed Izuku with blood, he fought on, bringing the villain to his knees. His last act as the Number 1 Hero was to defeat this crazed villain and save the life of a young boy, even as weakened as he was.

The laughter continued as the villain approached, the flames shedding light upon him. Izuku felt a cold dread run down his body as he recognized that laughter. He'd just heard it not minutes ago.

"No." His voice was hoarse. "It can't be you. All Might defeated you. How are you-!?"

The villain raised his weapon, the blade whirling, but suddenly Izuku's vision seemed to stretch as it gave way to darkness. He heard a distant voice before he found himself face down in the snow, back outside the cave.

As he picked himself up, his hand brushed against an object. He grabbed it, realizing it was a flashlight. He turned it on automatically as he stood before he choked on a scream. He dropped the flashlight, but the image was already seared into his brain. The snow in front of him was caked in red as the severed body of someone hung from the branches. Shaking, he picked up the flashlight and forced himself to examine the body. The clothes had been stripped from him, leaving his flesh and blood to freeze up in the extreme cold. The lower half of the body hung upside down while the upper body hung upright. Below him, in the red snow and leaning up against the blood stained tree trunk, was his clothes and equipment. Izuku wanted to hurl when he realized who this probably was.

Pro Hero Turnback.

Something heavy moved through the snow behind him and Izuku turned around, already knowing who he'd see. The very monster he thought had been defeated. The monster he'd seen in his dreams for years since that day. He'd gone to great lengths to overcome that fear, that intense feeling of helplessness caused by this one man. He'd thought he'd gotten over it all, but with him standing before him, he now felt that same fear again.

"How?" He uttered, trying to stop his hands from shaking.

Laughter again as the hulking figure stepped into the flashlight's beam. He wore a snowsuit colored with green and purple colors with half melted skulls emblazoned on each shoulder. Combat boots pressed into the snow with similar skull designs serving as knee pads. He was extremely well built and at his side hung his favored weapon of choice; A heavy duty double-bladed chainsaw dripping with highly toxic and corrosive poison.

"Izuku Midoriya, the little boy All Might protected until his very last breath." Pure white teeth grinned at Izuku from a face dripping with poison, his hair a sickly green color as it oozed the substance. Drops ran down his clothes and hit the snow, sizzling upon contact. "Look at how far you've come since then."

Izuku took a step back, his fear and anger battling to take control of him. "How are you here!?" He demanded. "You should be rotting in Tartarus!"

"Tsk." The villain shook his head, more poison flying and hitting the snow. "Don't remind me of that accursed place." He raised his chainsaw and revved it, his grin widening. "I was defeated by All Might years ago. My goal was to kill everyone in that damn place, but I failed to do so. I killed everyone but one." He approached Izuku, forcing him to take more steps back. "Everyone but you. All Might was able to save you, his last act as a hero. How… heroic."

Izuku dropped the flashlight as One For All blazed through his skin. 30%. "Is that why you're here?! This whole mess, the murders, all of it because… because you're mad you lost!?"

"Nah, nothing so much as that." The villain infamously known as Toxic Chainsaw hefted his signature weapon, poison being sprayed around him from the whirling blades. "I like killing. It rejuvenates my soul. I've taken my time since I escaped Tartarus, waiting for the perfect opportunity to begin killing the masses once again. So how fortunate I felt when none other than you were to show up in the town of my choosing." He took a huge step forward, a maniacal gleam in his eyes. "So let's see if you have what it takes to do what All Might couldn't that day, and save everyone you can before I slaughter them all!"