Rintaro is a high school student and self-described hikikomori who withdraws from society following his grandfather's passing. He spends his days in the quiet sanctuary of Natsuki Books, a secondhand bookshop filled with classic literature. Preferring books over human interaction, he possesses an extensive knowledge of literature but struggles to connect with his peers.

Tiger is a large ginger tabby cat capable of human speech. He arrives at the bookshop with a sharp-tongued, impatient demeanor, bluntly assessing Rintaro's reclusive habits. Functioning as a mystical guide, he possesses the ability to open portals to strange labyrinths where he claims books suffer mistreatment.

Sayo is the diligent, pragmatic class representative at Rintaro's high school. She presents a socially confident exterior, which contrasts heavily with Rintaro's withdrawn nature. Despite her scolding tone regarding his truancy, she demonstrates genuine concern for her classmate's well-being and gradually develops an interest in his literary world.

The Elderly Woman projects a cold, emotionless exterior while holding immense influence over the final labyrinth. She challenges idealistic views about reading, confronting visitors with visions of hardship to question the morality of their actions.

Rintaro's grandfather was a former university academic who left institutional life to run a quiet secondhand bookshop. He raised Rintaro and imparted a profound philosophy about the inherent power of literature. His carefully curated collection of non-commercial classics reflects his belief that books serve as lifelong friends.

Ryota is a popular high school senior and a regular customer at Natsuki Books. He expresses genuine sadness over the shop closing and actively encourages Rintaro to return to his classes.

Rintaro's aunt is a practical woman who steps in as his new guardian. She expects Rintaro to close the family bookshop, pack up the inventory, and relocate to her home.

The Imprisoner is a famous intellectual critic who views literature primarily as a tool for status. He boasts a collection of over 57,000 books, keeping them locked inside individual glass display cases. He believes that reading a book once is sufficient and considers rereading a waste of time.

The Mutilator is an overweight scholar who directs a vast research facility. He obsesses over efficiency, practicing a method he calls the streamlining of reading. To save time for busy modern people, he condenses classic masterpieces into single-sentence summaries.

The Seller is the cynical president of a massive publishing corporation. He operates under the strict philosophy that books are merely expendable consumer goods, choosing to publish only guaranteed bestsellers and sensationalized content to maximize corporate profits.