Kurihara is a draftsman with a keen interest in mysteries. He assists Uketsu by interpreting floor plans and offering theories as they delve deeper into the story's central mystery.

Yuzuki is a secondary protagonist with a personal quest to reconnect with her family amidst mysterious traditions. Her involvement becomes pivotal in unfolding the story's key events and revelations.

Shigeharu is portrayed as a key villain within the narrative, linked to the sinister traditions explored in the book. His character embodies themes related to power and control.

Keita emerges as an essential figure pivotal to resolving the novel's central conflict. His backstory and actions significantly influence the storyline and character relationships.