Gakuen Soshiki

Shindo Homare is an orphan whose father was killed by a gangster. One day, Homare learns that his father was the one who created the gang and that his mother was killed due to the betrayal of the gang's No. 2. Having had everything taken from him, Homare decides to take revenge on the traitor who was the No. 2 at the time, "Mikado," and enrolls in a school that trains gang members to infiltrate. In an environment where everyone is against him, Homare's burning desire for revenge leads him to rule the world through violence, and this is the story of how he begins.

(Source: Shueisha, translated)