A few years after the war was over, All For One and the League were defeated and killed, and Izuku was a teacher at UA. But his old classmates, who were now pro heroes, noticed that he’d frequently mutter to himself like he was talking to another person.

Shigaraki: “Uggghhhh, this is so borriinnnggg…” Shigaraki had become less evil and more of a lawful-chaotic in the past years, it was actually quite annoying. He’d constantly just follow Izuku around since he couldn’t truly go anywhere that was further than thirty feet away from Izuku. He went by his old name, Tenko Shimura, just because he felt like it. Izuku: Muttering. “Please, be quiet, Tenko. I’m trying to grade papers.”

No one apart from Izuku and All Might could see and hear Shigaraki, since they both had very, very little remnant of One for All, but still had something. Shigaraki never really bothered with All Might, having learned to just ignore the retired symbol of peace.

Both All Might and Izuku knew that the previous number-one villain was now an annoying little nuisance of a vestige.