Neighbor, whose given name is not revealed but whose surname is Kurosu, is a junior high school girl living in the apartment next door to the protagonist Sasaki. She is frequently referred to simply as Neighbor or Otonari-san. Her background is marked by neglect from her mother, which leads her to spend much of her time sitting alone outside her apartment door, where she often encounters Sasaki. This isolation has left her without friends at school and deeply lonely.

Personality-wise, Neighbor displays yandere traits, forming an obsessive and intense attachment to Sasaki. Her motivations revolve around a desperate desire for affection and connection, specifically wanting Sasaki to feel desire for her. This longing drives her actions throughout the story.

In the narrative, Neighbor participates in a deadly game between angels and demons, aligning herself with the demon side. This involvement suggests she possesses some form of supernatural ability or power within that conflict, though specific details of her abilities are not extensively detailed. Her role is a key supporting character who becomes increasingly entangled in the supernatural events surrounding Sasaki.

Her primary relationship is with Sasaki, whom she views with obsessive love. While Sasaki is generally kind and concerned for her well-being, he is often unnerved by the intensity of her feelings. There are no other prominent relationships noted.

Developmentally, Neighbor transitions from a lonely, neglected girl to an active participant in the death game, embracing her yandere nature as she seeks to fulfill her wish. Later story arcs hint at her becoming a VTuber, indicating a continued evolution of her character and a search for new forms of connection. Her notable abilities stem primarily from her involvement in the angel-demon conflict, allowing her to engage in battles within that realm.