Sun-Ken Rock(2006)

Sun-Ken Rock

Ken Kitano has lost everything. He's lost his family, his dreams, and even his first crush, Yumin, who suddenly left for Korea to pursue her dream of becoming a police officer. He spends his days getting into one meaningless fight after another, but one day, after learning Yumin actually managed to make her dream come true, he decides to follow in her footsteps and head to Seoul. Only, instead of becoming a cop, he ends up catching the attention of a street gang and becoming their boss! Suddenly, his strength, values, and beliefs are put to the test as he navigates a new life that he's determined to keep a secret from Yumin, a cop to her very core.

(Source: Kodama Tales)

Notes:
- Includes nine extra chapters.
- Includes the one-shot "Trigun: The Lost Plant"