Leviathan (смешанная)

Shigaraki Izuku never intended to be a hero per-se. However, his quirk didn't exactly left him many options besides heroism. There was always the option to follow in his father's footsteps, but if the bastard didn't even acknowledge him as a son, he might as well rebel against him in any possible way.
And if Izuku decided that the best way to do so was to study under his father's mortal enemy to be the very thing his father hates the most? Well, then there's no blaming anyone but All For One.
OR: Midoriya is All For One's son.
Notes: (See the end of the work for notes.)
Chapter 1: A moment in time Chapter Text "Why's it that the old man couldn't defeat you?" Izuku asked as he leaned back against a wall, arms crossed against his chest as he tried to figure out how the hell All For One lost to a man who punched his way through any situation.
Instead of Toshinori, though, it was Mirai who answered. "Because All For One couldn't steal his quirk. It's locked into a secondary quirk that can only be passed through free will."
At that, Izuku laughs. And laughs until there's tears in his eyes. Nighteye looks at him like he's grown a second head while Toshinori just take a step back. That wasn't a laugh of a teenager. It was almost as scary as his laughs. "So that's the difference!" Izuku cleans the corners of his eyes where a few teardrops ran. He's not smiling anymore.
"What do you mean by difference?" Sir gets up from his chair, leaving paperwork behind. A chill runs down All Might's spine and he has to focus not to force his buffed form out of fear.
Mirai never leaves paperwork unfinished.
"He can't grab your quirk, but I do. In fact there's several of them. Seven, if I'm not mistaken," Izuku explains while looking at Toshinori's chest. Although one could argue that he was actually looking through