OSU! KARATE CLUB

Matsushita Tadashi is a second year student at Kangokou High School (in Osaka, Japan) and a constant target of Kangokou's numerous bullies who beat him up routinely after school. He is accompanied by his best friend Saitou Takaki, who is also constantly harassed. As the pair grow increasingly tired of being victimized they decide to join the titular Karate Club, which is notorious throughout Osaka's youth gangs for training and producing the city's most hardened and toughest teenage thugs while maintaining the facade of a legit school sports club. But when they join the club, they find themselves picked on just as much if not worse by the club's current members. — Description from AniList community (anilist.co).