Kyotaro Hikawa is an ordinary high school student trying to live a normal life despite being the son of a Yakuza boss. His world is disrupted when Kumiko Shizuki, a half-sister he has never met, suddenly appears. Kumiko is searching for a man with a centipede tattoo who killed her loved ones in the past, and she drags Kyotaro into her quest for revenge.

The story is set against the backdrop of the Japanese Yakuza underworld, where the Hikawa family’s criminal enterprise is entangled with other clans. Kyotaro and Kumiko must navigate the violent politics of the syndicate while dealing with their own complicated relationship. Their half-sibling bond is tested by a growing romantic tension, which is complicated by their shared quest and the dangerous secrets that surface.

The narrative follows several arcs that explore Kumiko’s hunt for the centipede-tattooed killer, the shifting alliances and betrayals within the Yakuza, and Kyotaro’s reluctant involvement in the family business. Along the way, the series blends action, drama, and romance, with explicit content and moments of dark humor. The series covers 59 chapters, concluding the story of revenge, family loyalty, and the violent consequences of the underworld.