Tokyo Revengers

Takemichi Hanagaki leads an awful working adult life: he lives in a crappy apartment with thin walls, he's a virgin, and his six-years-younger boss treats him like an idiot. And then he learns that his former school girlfriend Hinata Tachibana, the only girl he ever loved, has been killed by a street gang. Suddenly, he travels in time back to his middle school days. To save Hinata, and to change the life he spent running away, hopeless Takemichi must aim for the top of the Kanto region's most sinister delinquent gang.