Fandom: My Hero Academia

He has PTSD from Bakugo's bullying.

I mean, it's not very surprising given that Bakugo LITERALLY told him to jump off a building.

It's mostly verbal cues; Izuku does his best to keep his reactions internal, but at times, explosions startle him a bit more than they startle the average person.

Despite having PTSD from all that he did, Izuku doesn't blame Bakugo for anything he did and holds no spite against him.