Seikei is the son of a wealthy tea merchant living under Japan's rigid caste system. He secretly aspires to become a samurai and holds himself to their strict code of conduct, even though society demands he inherit the family business. His keen observation skills and natural bravery draw him into a mysterious investigation at the Tokaido Inn.

A legendary and incorruptible samurai judge appointed by the shogun. Ooka relies on psychological insight rather than force to solve crimes, setting him apart from many authority figures in his era. He maintains a simple rock garden that reflects his contemplative nature and is quick to recognize genuine virtue regardless of a person's social class.

A powerful and arrogant daimyo traveling to Edo to present a brilliant ruby to the shogun. Hakuseki relies on his hereditary high status to demand obedience and free goods from merchants. He behaves with routine cruelty and impulsiveness, while his crude handwriting and lack of honorable conduct provide a contrast to the noble ideals expected of a samurai lord.

An agile member of a traveling kabuki troupe who possesses unusual proficiency with a sword. Bearing a distinctive scar across his right cheek, he harbors a mysterious past tied to the samurai class. Despite working in a culturally disrespected profession, he adheres strictly to his own personal code of honor and faith.

The perceptive daughter of a paper maker. She shares a chilling ghost story about a flesh-eating monster with Seikei, sparking his active imagination. When she faces false accusations of theft, her perilous situation tests the courage and honor of those around her.

A pragmatic tea merchant from Osaka who wants his son to learn the family business. He strictly adheres to the expectations of the Edo caste system and views poetry and samurai ambitions as useless distractions for a merchant class family.

A traditional samurai serving under Judge Ooka. He exhibits the common prejudices of his class, viewing merchants as inherently lazy or dishonest. He frequently doubts the wisdom of the judge's decision to trust a boy from a lower caste.

A young boy working for the traveling kabuki troupe. Raised in the theater world, he is perfectly content with his social station and actively cautions others against possessing ambitions that conflict with societal expectations.

The highest-ranking military ruler in Japan, whose laws uphold the rigid caste system that separates samurai from merchants and farmers. He values tradition and order, requiring absolute loyalty from his daimyo subjects while holding ultimate power over their lives.