Y'all I'm so sorry this chapter is all just one massive history lesson. It's all lore DJKSKLD stg I get way to into this sometimes bro

Third person pov

In the beginning, merfolk were not much more than just that. 

They were not magicians or warriors, nor were they sirens or seers. They were simply creatures born from the sea's core, with the upper body of a human and the lower of a sea creature. Though Atlantis had only ever seen glimmering fish species amongst his pod, he'd heard tales of shark fins and octopus tentacles, dolphin tails and eel bodies. Their race, centuries ago, was plentiful and diverse in a way Atlantis had never gotten to know it to be. Though their magic came shortly thereafter, the matter of the fact was that they were just mer first.

The ocean loved them. It loved them, it loved them, it loved them. It gave their race life and meaning, building for them a grand kingdom that has since been lost in time. Atlantis was said to be a momentously large city made of smooth blue stone that reflected the many colors of the illuminating coral situated within and around it. It was a safe-haven for merfolk of every type. It was known for its harmony and beauty, and for the artful culture that was born within it. It was a simple time where peace reigned, when mer were plentiful and their existence was not known to those who dwelled on the surface.

"The City of Atlantis was ruled by a King and a Queen. They're said to be the very first of our kind-- though, it's not known if this is true." Atlantis explained wearily, a fresh cup of hot chocolate in his hands. The mess on the carpet had been cleaned up, leaving only a vague brown stain in its wake. "What's certain is that they were beloved and trusted, benevolent and pure-hearted in every way. The sea loved them endlessly, just as it does all mer. I was always told that the King and Queen were the sea's spirit in mer-form. They're described as powerful, kind beings with glimmering gold tails that would glow even in the deepest parts of the ocean."

This was not a story Toshinori knew, and he wasn't sure how to feel about that. The Number One Pro shifted in his seat, heart thundering. He had always known One For All was ancient, but to think it wasn't a quirk at all was... it was astonishing. 

"There are vague depictions of him seen in Greek mythology on land." Hitoshi noted. The boy leaned back against the couch, looking nearly wistful. "Though our King and Queen were nothing like the Poseidon and Amphitrite written about here, they're the most likely to have originated from our story."

Aizawa nodded, supposing that made sense. Poseidon was the most well-known god of the sea. Only Poseidon was reportedly known for his bad temper, and according to Atlantis and Hitoshi, this King of theirs was nothing like that. Or maybe he was. There was a thrumming in him and his husband's bond that told him this story was going to take a dark turn, as most histories tend to. He pulled the mer a little closer, not caring how Toshinori stared at their matching tattoos with new light.

"The ocean is giving. So giving, in the end, that it felt gifting life and home to its children wasn't enough. It wanted our race to have everything. It wanted us to have abilities beyond comprehension." Atlantis continued with a small smile. It came out looking tired. "The sea gave our King the ability to create, and our Queen the ability to take as a fail safe. With this, they were able to grant their subjects with powers of their own. The King and Queen both planned and came up with boundless abilities. The power to heal no matter how grievous the wound or illness, and to shift even the strongest tides. To bring forth devastating weather, and to enchant with a voice. To grow and shrink in size, to see into the future, to shapeshift and create illusions."

"There was one power for every one mer. Though, we all gained the ability to participate in rituals, even if our magic isn't always the best suited to them. It's why I was able to help Atlantis heal you. Still, as a basis, no mermaid or man could have more than one magic." Hitoshi agreed, leaning forward so that his elbows were propped on his knees. He glanced at his cousin. "At least... At least not until the Queen became pregnant."

Toshinori felt something in him go cold, and his quirk twisted in a way it never had before, as though it knew what was to come. He resisted the urge to grasp at his chest and instead kept his eyes trained on Atlantis. The merman looked notably stressed, his brows creasing. Aizawa was visibly worried for the man, the arm around his husband tightening comfortingly to try and relieve some of the stress.

 "The King and Queen had a son. He could have more than one type of magic, and though he couldn't create, he did possess the ability to give and take." Atlantis' face twisted a little, and he looked... he looked sad. Toshinori scoldingly reminded himself that this was the man's history. That this had all happened, and that it meant something to him. And it should mean something to Toshinori too. "The King and Queen loved him dearly. They poured ceaseless power into him. So much so that he became greedy without them noticing, wanting for more and more."

It hit Toshinori exactly who this son was. The ability to take and give. To host more than one ability. All For One... was much older than he'd thought.

"Why... Why didn't the sea take the power back?" Toshinori asked, clasping his hands together so tightly his knuckles went white.

"The sea is so giving that it cannot take." Hitoshi sounded fond. He looked down into his near-empty cup of coffee, taking a deep breath. "Once it gifts, it... I've never heard of it taking."

"Me either." Atlantis' smile was strained. He cleared his throat a bit, his grip on his cup tightening. "Things were peaceful, for a time. A few years passed before the Queen became pregnant again, and another boy was born. He was... he was a lot weaker than his older brother. He could not be given multiple abilities. His brother and parents loved him unconditionally despite this, and it was his older brother who gifted him with a strengthening power in hopes of making him healthier." 

This... This was a story Toshinori knew. He felt pale, his heart thundering. Who was Nana Shimura really? Why choose a human? Why was All For One on land?

"The King and Queen grew old, and when they passed, their eldest succeeded the throne." Atlantis said. "He abused his power. He became controlling and corrupted almost immediately upon the passing of his parents. Without his father there to create abilities for him, he began to take the magic gifted to his subjects for himself." 

"The mer began to flee Atlantis because of this. It's why it's called the lost city. It's because they all ran in an attempt to save their lives and the magic that had become such a vital part of them and their identity." Hitoshi added. Atlantis nodded, and Aizawa felt a little sick, yet a little amazed at the same time. This was an entire history no one else knew-- that had happened, and was real, and he was hearing it.

"His younger brother tried to stop him. It was then that the eldest found out he couldn't forcibly take his sickly brother's power. He wounded him fatally with magic during their fight, and with Atlantis already vacated, the few healers that existed had long since left, deeming their power too valuable to risk it being taken." Atlantis said. "The younger brother... he found out that though he could not create or take, he could give, even if the mer already had an power. So that's what he did. He passed his ability on to a close friend-- maybe a lover-- who had stayed around, begging him to stop his elder brother before he destroyed our race."

"S-So... So then why is All For One on land? How is he on land?" Toshinori sputtered. He leaned forward a bit. "I had thought for certain that I defeated him, but you said that this... that my legacy would--"

"The power was called otu maka mmadu niile, or One For Everyone. Overtime this evolved into One For All, a power passed on and on that wont rest until its enemy, All For One, is destroyed." Hitoshi said. He looked grim as he gazed at the pale Number One Pro. "If you still have it and it still works, then he's still around according to our history."

And if that wasn't terrifying, Aizawa wasn't sure what was. How many centuries was this being? What sorts of powers had they been gifted by their father, the beloved King? To think someone with that much power was out there was astonishing, and to think that larger-than-life All Might couldn't defeat them was even more shocking. Aizawa never would've assumed the mer race had such a bloody past, but he supposed humans were no different.

"He did not come to land by choice, originally." Atlantis pushed himself further into Aizawa's side, his breaths a little shaky. All For One was still around. "He... figured out a way to take a mer's tail. He would banish mer from the sea and damn them to a life on land in which it was nearly impossible for them to fully return to the ocean. The sea was enraged and used a piece of it spirit to curse All For One to the same fate, in turn losing its ability to give gifts."

"He blamed his younger brother and though he no longer had a tail, he began to hunt the mer with his brother's power mercilessly over the years. He encouraged humans to hunt us, too, creating the fantastical tales you know today." Hitoshi grimaced. "It's why our race has almost gone extinct. Still, All For One never was able to kill off his younger brother's magic, which grows more powerful each time its passed on."

"Our grandmother, Nana Shimura, was the last to have it before you. I... I suspect you know this. She set out for land to hunt him down herself. Our pod was dwindling and he knew she was in it, and his relentless attacks killed many in our family." Atlantis sounded sad, his gaze a little distant. Toshinori's heart wrenched as the news settled. His mentor had been forced to leave her family for their safety. Her family, who'd been killed for this... this legacy. "She ran to protect us and stop him for good. We thought... We thought she succeeded and had perhaps lost her tail in the process, but it seems that was incorrect." 

"The fight where you got your injury happened around the time our pod was attacked, scattered, and killed." Hitoshi's voice was quiet. "It wasn't something... we didn't put it together-- him and the event. It all happened so fast that I wasn't sure what happened, and neither was Atlantis."

The implications were... terrifying, and devastating to boot. All Might felt sick. When he'd wounded All For One, had the villain become enraged and gone after Nana Shimura's family? Tracked them down and ruined them for good? He felt immensely nauseous thinking about it. Though he never would've suspected his mentor was a... a mermaid, she had still cared for him like a mother might've, training him and trusting him with her legacy. Her legacy, which was so powerful and ancient and definitely not something quirkless teenager Toshinori Yagi was worthy of.

Aizawa felt his tattoos begin to itch alongside Atlantis' agitation. He wished there was something he could say, but he knew it wasn't his place. Instead, he tried to focus on getting a better understanding. He poured himself into their bond, wrapping around Atlantis' emotion and absorbing it. The tension, the stress, the weight behind this story. He took it all it, and Atlantis gave him a small smile for it, seeming to get exactly what he was trying to do without him having to use words at all.

"He hunted our kind for centuries until there were hardly any of us left." Atlantis sounded tired, and Aizawa couldn't say he blamed him. Finding out the destroyer of your race was still alive had to be terrifying, and rage-inducing if nothing else.

"I think his coming to land is where the birth of quirks came from. Reading about the dawn of quirks, I... I think after he was satisfied in his hunting of the mer, he decided he wanted power on land too." Hitoshi admitted. Atlantis turned to him, curious and unknowing of land's history just yet. Toshinori peered at him in a startled manner as well. "My theory is he gave powers to tons of random individuals to cause unrest and general chaos, and these abilities shifted and changed over time to become the quirks we know today, growing more complex and powerful as they evolve. The unrest would've given him a real chance to weasel his way into several influential positions and to create an elite network. A new kingdom."

A new Atlantis.

"I... I need to make some calls, I think." Toshinori's voice came out distant. Atlantis sniffled, wiping at his eyes and shaking his head. Hitoshi hunched into himself slightly, throat tight. "I need... I need to make a lot of calls."

~~~~~~~~~

It's not easy to get your tail back after it's taken, but that doesn't mean it's impossible.

"Tomura Shigaraki." Kurogiri's tone wavered as the young man stared at himself in the mirror. Kurogiri couldn't see his face, but he could see the way his body shook with barely-concealed sobs. His hair had gone almost completely black now, fading into his usual light blue at the ends. It didn't appear to be spreading anymore than that, and it was oddly fitting in a way. The warp-gate user flickered slightly, adam's apple bobbing beneath his mist that never seemed to dissipate. "Is something wrong?"

He was met with silence for a moment, but Kurogiri is nothing if not patient. He stood in the doorway, unwavering in his presence as Tomura processed. He'd been in a daze since waking up, stumbling around, not quite replying when his name was called. Tomura was subdued and confused these days, almost as though he wasn't sure where he was at times. He didn't play his video games anymore, and his bouts of rage had almost completely disappeared after their few visits to the ocean.

It was a small miracle that Sensei oftentimes left Tomura to his devices. A check in right now would immediately give away that something was wrong. Sensei could see better than most, but not in any sense that would give away the drastic changes in Tomura's appearance. Colors were not something Sensei could pick up on anymore, and though Kurogiri would die before saying it out loud, he was endlessly relieved. At most he would notice the lack of dryness in the young man's skin. It was a bridge they'd have to cross when they came to it. If they came to it. Kurogiri privately hoped Sensei wouldn't think enough of it to bring it up.

That was all besides the point, however. The fact of the matter was that Sensei could not be allowed to talk to Tomura Shigaraki in this state. Kurogiri dreaded to think what would happen if he noticed his spacey behavior and lack of petty anger.

"I don't... I don't think that's my name." Tomura's voice came out so quiet and broken that Kurogiri almost didn't hear it. The warp-gate user didn't move-- didn't even breathe. He did not dare mention that Kurogiri did not feel like his name either. He knew well and good that his identity was given to him, and he suspected it was the same for Tomura. Neither of them could recall anything before Sensei. This was not a coincidence, but it was something not to be questioned.

"Does it have something to do with the boy from the Sports Festival? Hitoshi Shinso?" Kurogiri could not curb his curiosity or his concern, which festered hot in the pit of his stomach. If he got more information, perhaps he could help.

"Yes... Yes, it is. It is. I think I know him, and I think... I think he knows me. I just don't know... I don't know how I got here. I'm not supposed to be here. I'm not. I'm not supposed to be here." Tomura said in an insisting, disjointed sort of way. Kurogiri's breath hitched as the young man whirled around, face distraught, tear-stricken, and endlessly confused. The warp-gate user froze as the young man shook, bringing his hands up and digging them into his dark hair. "Wh-What is my name? I don't... I don't know my name, Kurogiri. Wh-Who am I?"

Kurogiri couldn't find the breath to answer. Because Tomura Shigaraki was staring at him with a set of eyes there were no longer the blood red color he'd always known them to be. They were now seafoam green, and the storm raging behind them spoke of a past before the villain he was now. A life he'd lost but still yearned for. A different identity, and a family, and... 

And Kurogiri wanted to help him find that. Sensei had created him for the sole purpose of taking care of Tomura Shigaraki. He was ordered to keep him happy, healthy, and safe. The way Kurogiri saw it... well, the young man he'd nurtured over all these years wasn't any of those. 

Not yet.