Airi Akizuki is the younger daughter of Kayoko Akizuki and the stepsister of Marina Akizuki, sharing no biological father with Marina. She harbored intense hostility toward her new stepfather, Kouzou Akizuki, subjecting him to continuous verbal and emotional abuse for over a year to drive him from the household, resenting her mother's remarriage and refusing to accept Kouzou as family.

Physically, Airi is a teenage girl with blonde hair styled in twintails, blue eyes, and a slender build. She attends school as a popular and desirable newcomer despite her recent arrival. Her interests include cosplay, though opportunities are limited. She forms a close friendship with classmate Sana Kuranaka.

Airi's relationship with Kouzou shifted dramatically after he retaliated against her mistreatment by forcibly administering an experimental aphrodisiac spray. This rendered her unable to resist his subsequent sexual advances, leading to repeated non-consensual encounters. While initially resisting these violations, she gradually developed a physical dependency and psychological attachment to Kouzou. Her feelings evolved into possessiveness and jealousy, especially when Kouzou paid attention to other girls like Sana or Marina. She openly declared Kouzou her exclusive sexual partner and actively competed for his attention.

Later, Airi's dynamic with Kouzou grew more complex. She displayed genuine affection and sought authentic emotional connection, yet remained aware of his continued use of aphrodisiacs to manipulate her. During a family trip ("Re-born"), she expressed displeasure upon learning Marina would join them later, leaving her alone with Kouzou. Despite attempts to avoid isolation, Kouzou drugged her during a train journey, reigniting her internal conflict about whether his attraction depended solely on chemical coercion.

Her relationship with Marina included sexual encounters, sometimes initiated through Kouzou's involvement, including three-way scenarios. Airi also exhibited exhibitionist tendencies, engaging in sexual acts with Kouzou in risky public settings like train bathrooms, beaches, or ocean fronts, driven by the thrill of potential discovery.

A significant moment occurred when Airi orchestrated revenge against Kouzou for his past assaults: she buried him in sand at a beach and deceived a homosexual lifeguard into performing non-consensual oral sex on him while she watched from a distance. Ambiguity surrounds other incidents, like an encounter at a remote bus stop during heavy rain. After engaging in sexual acts with Kouzou, she later denied the event occurred, leaving its reality uncertain.

Her character experienced pregnancy as a result of the non-consensual relationship, contributing to the cyclical nature of her trauma and dependency.