Sun-Ken Rock

The story revolves around Ken, a man from an upper-class family that was orphaned young due to his family's involvement with the Yakuza; he became a high school delinquent known for fighting. The only thing that motivates him to take action is through his romantic affections for a classmate, Yumi. After learning she decided to move to Korea to become a police officer, Ken leaves his life in Japan behind and tries to follow in Yumi's footsteps; due to unforeseen circumstances, he incidentally becomes the head of a local gang and tries to hide it from Yumi. As the leader, the gang is renamed the Sun-Ken Rock Group.

(Source: Wikipedia)

Included one-shot:
Volume 12: Trigun: The Lost Plant