Oniyan

Shigeru Yoshida, a.k.a. "Oniyan," is a middle schooler with a scar on his forehead and a temper! He is as free-spirited as a baby and hates compromising. Even in fights he can't win. He bravely takes on challenges with his amateur judo skills, guts, and wiles. He and his friends were ferried from a branch school with only 15 students to Tosa Minami Junior High, the former naval preparatory school. In this school where the public morals committee rules using fear and politics, Oniyan howls with vigor!

(Source: Beaglee, translated)

Note: Serialized as Oniyan (鬼やん) in Weekly Shounen King. The title was changed for the complete volume release.