沼淵 虎造

He is the leader of the gangsters of the city, known as undefeated. His "people" and others call him "Boss" because he runs a gang that rages in several schools. He considerates himself as a rival of Tsukumo.
His war symbol is a tiger.

Even if he looks extremely cold, he can be "considerate" with the people he likes. The day he learns of Natsuki-sensei's death, he breaks Tsukumo's mouth so he can get out of his depression and become strong again.

Without him, Tsukumo would not have sought - nor thought - to go back in time.

His relationship with Tsukumo - after their fight - is very similar to that of Vegeta and Goku in Dragon Ball Z.