Sun-ken Rock

is a manga written and illustrated by Boichi. The manga was serialized in Young King from April 24, 2006 to February 22, 2016.

Plot
The story revolves around Ken, he's a Japanese high school delinquent that was orphaned young due to his family's involvement with the Yakuza. The only thing that motivates him to take action is through his romantic affections for a classmate, Yumin (the daughter of the very Yakuza group that killed Ken's parents). After learning she decided to move to Korea to become a police officer, Ken left his life in Japan behind and tried to follow in Yumin's footsteps; due to unforeseen circumstances, he incidentally becomes the head of a local gang and tries to hide it from Yumin. As the leader, the gang is renamed the Sun-Ken Rock Group. At the first, the gang only consisted of few members and didn't even have a base. As the story progresses The Sun-Ken Rock gang becomes bigger as they recruited new members and take over other gangs' territories and investments. The Sun-Ken Rock Group acquires an MMORPG company, a large casino, one of the biggest television media companies in Korea, as well as garnering political favors (making them the most powerful gang in Korea). However, throughout all of this, Ken has done his best to evade revealing himself to Yumin as a gang leader as she despises gangs. Ironically, Yumin was groomed to become an advanced plant in Korea to help her Yakuza group lay the foundations to expand their hold into South Korea; due to Yumin's refusal to join the "family business," their plans were stalled as various members either tried to take her back to Japan or try to get her back into Yakuza control. In between Ken's rise, he and Yumin got closer and Yumin started to have feelings for Ken. However, things were always complicated by the interference of either Ken's gang activities and/or Yumin's Yakuza connections. The turning point in the story was when she was kidnapped by her own group and Ken was exposed as a gang leader in his attempts to rescue her from his greatest rival, Kim Ban Phong (a Vietnamese-Korean that has a vicious score to settle with Ken).

Official
http://sunkenrock.com/