The New All For One

Successor

"H-huh?!" Both Izuku and Small Might blurted out in unison, the latter having more blood coughed up. But that was beside the point, All For One had just suggested Izuku be the successor for both of their Quirks.

"What? Having both at once isn't impossible, otherwise, I wouldn't have spent so long trying to get [One For All] into my possession."

"It's not that!" Yagi exclaimed, "Why would you even suggest that? I mean, how do we know this isn't some trick?"

"Yagi, I'm dying here. What could I possibly do?" All For One asked sounding exasperated.

"Take over my body," Izuku stated getting three sets of eyes on him. Well, it was actually only two but you know what I mean. "What? I've seen Naruto, how do I know it's not some ploy to pull an Orochimaru."

Yagi just nodded in agreement even though he had no clue what the young man was on about. All For One looked impressed, muttering something about people still watching that particular anime.

"Gotta agree with the kid. How do we know it's not some play so you can become the immortal Demon Lord." Gran Torino questioned.

"You don't. But I can assure you I'm not like the snake. If anything, the result would be a win-win for all of us." The villain simply said. "The young man gets the means to become a hero. I'll be dead, so I won't be a problem any longer. And I... I get to be reunited with my younger brother." He explained.

"Your brother?" Izuku enquired.

"The first user," Yagi said. "But how?"

"It's rather simple really. I'm sure you are aware of the ghosts inside [One For All]." Yagi nodded, "During my earlier years I began to have memories from lives that were not my own. Soon after I discovered another plane of existence were vestiges of people whose Quirks I had taken existed. You see, Quirks are a part of a human's soul, when I take a Quirk I'm also taking a part of the user's soul. The same is true for [One For All]."

"[One For All] accumulates not only power but pieces of the past user's souls within it as it gets passed down?" Gran Torino asked and All For One nodded.

"So then if a person was to be in possession of both Quirks then the respective "vestige worlds" of the Quirks would become one allowing for all the vestiges to interact. So then in the case of All For One's death, he would go to the vestige world and therefore be capable of reuniting with his brother because he would already be there." Izuku theorised.

"Exactly right my boy." The man smiled. "I know I'm not a good person, not by a long shot, nor was I the best older brother. But I love my brother, even if my idea of love is a little twisted. I suppose the idea of reuniting with him made me a little soft." He chuckled which turned into a coughing fit, making Izuku freak out.

"You, getting soft? Yeah right." Torino retorted.

"Well, my subordinates wouldn't have attempted to kill me if I didn't. Why else would I be out here with the bare minimum that's allowing me to live?" The ex-king questioned. "I also believe this young man would be a far better fit for [One For All] than the other candidate."

The statement made Small Might shocked, he know about the other candidate. But before he could question his nemesis, the man answered. "He would have died before being able to fully harness the power."

The three men looked dumbfounded and Izuku asked why the candidate would die, to which he responded, "Because he already has a quirk."

All For One went on to explain people aren't supposed to hold multiple Quirks, of course, there had been a few exceptions, but none of those were as strong as [One For All]. During his earlier days whenever the King of the Underworld gifted a second quirk to someone, after some time they lost brain function.