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, 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 also tries to follow Yumin's footsteps but due to unforeseen circumstances, he incidentally becomes the head of a local gang which he renames as the "Sun-Ken Rock Group".

At first, the gang only consisted of a few members with no headquarters, but grew bigger as they recruited new members and occupying other gangs' territories and investments as the story progresses. Investments include 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 does his best to hide the fact from Yumin due to her despisement of 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/