"Sun-Ken Rock" is a manga series that centers on Ken, a young Japanese man who moves to South Korea to pursue his love interest, Yumin, a police officer. Initially, Ken aspires to become a police officer himself to be closer to her, but his lack of qualifications leads him down a different path. He becomes involved with a local gang, quickly rising through the ranks due to his exceptional fighting skills, charisma, and sense of justice. Over time, Ken transforms the small gang into a powerful organization, the Sun-Ken Rock Group, which operates as a quasi-vigilante force, protecting the weak and challenging rival gangs.

The narrative explores Ken's internal conflict between his desire to live a righteous life and the violent, morally ambiguous world he inhabits. Yumin, unaware of Ken's criminal activities, remains a central figure in his life, symbolizing his connection to a more lawful and idealistic existence. As the Sun-Ken Rock Group expands its influence, Ken faces increasingly complex challenges, including betrayal, political corruption, and rival factions. The story delves into themes of loyalty, power, and the consequences of one's choices, as Ken struggles to maintain his principles in a world dominated by violence and greed.

Key characters include Ken, the determined and physically formidable protagonist; Yumin, the principled police officer who represents Ken's moral compass; and Taewon, Ken's loyal friend and second-in-command, who provides both comic relief and emotional depth. The series also features a diverse cast of allies and adversaries, each contributing to the intricate dynamics of the criminal underworld. The plot is driven by intense action sequences, strategic power struggles, and the evolving relationships between characters, creating a compelling and multifaceted narrative.