Kill Blue, Vol. 1

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!

Volume 1 of the Kill Blue manga series by Tadatoshi Fujimaki.