Kill Blue manga volume 1 features story and art by Tadatoshi Fujimaki.

Juzo Ogami's a legend. Even among hit men, his name sends shivers down their 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 never thought he'd find himself in… school!