An otherworldly, magical realist character, Tiger is a large talking ginger tabby that arrives unannounced to guide Rintaro. As a mentor, Tiger initiates the protagonist’s quest by leading him into a series of challenges that test his courage and beliefs about books.

Rintaro's class representative, Sayo is initially pragmatic and socially confident, contrasting with Rintaro's withdrawn nature. Her involvement in the story’s challenges develops from bringing Rintaro his homework into a deeper partnership reflective of her concern for him.

Though he is deceased before the story begins, he remains a guiding influence, shaping Rintaro’s philosophy and love for books. His past teachings about the power of literature continue to influence Rintaro's actions and beliefs.

An antagonist who embodies the vanity of reading for status, keeping a vast collection of books locked away and preferring quantity over meaningful engagement. He serves as the first thematic obstacle that Rintaro must overcome.

The antagonist of the second challenge, he reduces literature to basic summaries to cater to a fast-paced world, believing complexity is expendable. His methods challenge Rintaro to advocate for the intrinsic value of deep reading.

A representative of the commercialization of literature, he prioritizes sales over literary integrity and produces whatever content sells best. His perspective offers a critical view of the publishing industry's priorities.

The final antagonist, she symbolizes the neglected soul of ancient literature. Her challenges prompt Rintaro to articulate the enduring significance of books in fostering human empathy.