Tokyo Manji Revengers

Tokyo Manji Revengers summary:

Watching the news, Takemichi Hanagaki learns that his girlfriend from way back in middle school, Hinata Tachibana, has died. The only girlfriend he ever had was just killed by a villainous group known as the Tokyo Manji Gang. He lives in a crappy apartment with thin walls, and his six-years-younger boss treats him like an idiot. Plus, he's a complete and total virgin … At the height of his rock-bottom life, he suddenly time-leaps twelve years back to his middle school days!! To save Hinata, and change the life he spent running away, hopeless part-timer Takemichi must aim for the top of Kanto's most sinister delinquent gang!!