Juzo Ogami has never led a normal life. He was picked up by a criminal organization as a child and grew up to become a legendary hit man. But everything changes when he's bitten by a mysterious insect and becomes a teenager again! Can this battle-hardened assassin handle the rigors of middle school life?!

In the middle of a double date, Juzo abruptly reverts to his middle-aged body. And to make things worse, Noren is abducted while he's indisposed! Juzo follows her abductors and finds himself face-to-face with two members of the world's largest murder-for-hire syndicate. Will he and Tenma be able to pry Noren from their clutches?