Iijima Gosei, who was a weak and unremarkable delinquent high school student, was traumatized by his failure to save his sister during a major gang fight. Driven by the desire to become stronger, he committed himself to the world of mixed martial arts.

Years later, having become a world-class fighter, Gosei finds himself unable to challenge for the title despite his numerous victories, and he still regrets not saving his sister. When an old delinquent acquaintance offers him a fixed match, Gosei refuses and is tortured to death as a lesson to others.

He then wakes up back in his high school days, just before the incident involving his sister's assault. A professional fighter now finds himself among high school delinquents. The once weak errand boy has become the strongest overnight, shocking the local delinquents.

If he could return to his miserable past self and start his life over, what would he do? With overwhelming power, he aims to beat the most notorious delinquents and become the top among all delinquents! The revenge to save his sister and change his life begins now!