Yabou no Oukoku

Seigoro Tachibana, a law student at the University of Tokyo, is the son of a mistress and Seizo Tachibana, the leader of the largest gang in Kanagawa Prefecture. His goal is to conquer Japan's underworld, by violence if necessary. Together with his good friend Jin Kataoka, they set out to realize his plan, only to be confronted by Sejiro Tachibana, Seigoro's beloved older brother and his greatest enemy. The curtain rises on a fierce battle to the death between these men who are consumed with ambition!

(Source: Nihonbungeisha, translated)