Aya, also known as Arya, is a mysterious silver-haired boy who appears consistently throughout the narrative. He claims responsibility for cleaning up after Hazuki and Lilith's interdimensional activities and offers repairs on structures like Tamamonomae's Space Hall when damaged. A notable trait is his frequent cosplaying, appearing in different character or animal costumes during his appearances. His enigmatic actions serve as transitional elements between story segments through brief introductions or exits. At the conclusion of the main storyline, he closes a book containing the world of the Book Keepers, implying a higher-level involvement in the narrative framework. As the primary narrator, he provides connective tissue between disparate worlds and events.