KILL BLUE

Juzo Ogami’s a legend. Even among hit men, his name sends shivers down spines. There’s never been a job he couldn’t handle—that is, until the day he wakes up as a teenager! But how has his body transformed? To find out, he’ll have to infiltrate the one place he thought he’d never find himself in again…school! (Source: VIZ Media) — Description from AniList community (anilist.co).