Operating as a sex worker in Shinjuku's Kabuki-cho red-light district, the woman known as Father's Rival Woman forms a connection with Ichi, the protagonist manipulated by the father figure Jijii. Unlike others who bully Ichi for his social awkwardness and submissiveness, she shows him kindness. Their relationship features moments of mutual compassion, including Ichi giving her money for corrective nose surgery after learning of her self-consciousness.

Controlled by a pimp within a criminal environment dominated by yakuza, she occupies a vulnerable position. Her interactions with Ichi reveal her awareness of his emotional fragility, but she remains ignorant of his capacity for extreme violence under psychological manipulation. This unawareness leads to her tragic end: during one of Ichi's uncontrolled killing sprees, he murders both her and her pimp. Her death highlights the narrative's pervasive brutality and the collateral damage stemming from Jijii's exploitation of Ichi's trauma.