18+ Abashiri Ikka

The most famous and terrible family of gangsters in the whole world is about to dissolve, once it's revealed the mysterious secret of the third member, Kikunosuke, the most powerful member of the Abashiri. However, the almost pacific life of the Abashiri family gets complicated when Kikunosuke enters in one of the most prestigious elite schools, where instead of learning about art and culture, students must learn the most dangerous techniques for fighting and murdering, at the hands of cruel psychopath teachers. Only a few students manage to survive this hell of a school... but of course, in this occasion, the new student will be most terrible of the Abashiri, and things will no longer will be the same.

(Source: Wikipedia)