Known as "Door" or "The Doorway Girl," this character appears solely in the source material's first chapter and its adaptation. She serves as the guardian of a significant doorway that the protagonist must traverse. Production drawings showcase her detailed artistic design, with annotations emphasizing meticulous perspective and layout planning during her creation.

In her solitary narrative moment, Door initiates intense physical contact by seizing the protagonist in a tight embrace. She presses the protagonist firmly against her chest before permitting passage through the door. This brief interaction sequence constitutes her entire role.

Door neither resurfaces in later chapters or episodes nor receives additional elaboration within official media adaptations.