Hotaruko Kizuki is introduced as Ryou Inasa’s cousin, wielding a possessive, volatile nature. Her obsession with Ryou escalates from a schoolgirl infatuation into an all-consuming hunger, manipulating circumstances to imprison him in surreal spaces where she coerces repeated declarations of her supremacy over his former lover, Ruka, entwined with graphic intimacy.

Her lineage unravels twisted familial bonds. Hotaruko is later revealed as Ryou’s biological mother, with Itsuki as her mother and Ryou’s grandmother, positioning Mizuno—the cult’s deity—as both her brother and Ryou’s uncle. The family’s history hints at intergenerational incest, reinforced by a priest’s claim that Hotaruko and Mizuno’s births were essential to Ryou’s creation. A C-section scar marks her past, alluding to an unnamed child’s birth, likely Ryou. Surviving Bungo’s violent assault, her bandaged recovery underscores a resilience nurtured by the island’s macabre rites.

Driven by obsession and cult indoctrination, Hotaruko conducts sacrificial rituals, luring victims to their demise during ecstasy, repurposing their remains to animate mannequins. Her arc peaks by devouring Mizuno’s corpse, ascending to his throne with a grotesquely swollen abdomen—a visceral metaphor for inheriting his power and perpetuating the island’s cycle of violent dominion.

Her dynamic with Ryou weaves manipulation with warped tenderness, veering between psychological torment and possessive devotion. Fleeting vulnerability emerges through her desperate bids for his approval and her eventual physical decay, blurring the lines between antagonist and tragic figure.