Haruki Honma, brother to Natsume Honma and son of Kumi Honma, initially appears as a supportive figure while becoming the romantic focus of Aya Iseshima's longstanding crush. His persona unravels in the final episode, exposing him as a core conspirator alongside sister Natsume and cousin Miko Kazuki. Their plot seeks vengeance against Aya's family for historical wrongs: Haruki's mother Kumi and aunt Yumi Kazuki endured sexual enslavement after losing a martial arts tournament to Aya's mother, Suzuko Iseshima. This fuels Haruki's participation.

He shares a romantic bond with Miko Kazuki, his cousin and Aya's half-sister, strengthened by shared resentment. To manipulate the tournament and mask his involvement, Haruki employs a lookalike impostor as the public face of the organization. He later kills this decoy for attempted betrayal.

Haruki directly engages in Aya's psychological torment during the climax, joining Natsume and Miko to reveal their betrayal and the tournament's true purpose. His responsibilities include overseeing the transformation of defeated fighters into mindless sex slaves.

His demise occurs when Suzuko Iseshima intervenes to rescue Aya. Suzuko physically overpowers Haruki, snapping his neck alongside Miko and Natsume.