Name: Haru Yoshioka Gender: Female School: Aoi Prefectural High School (2nd Year) Lives with her mother. She has a sincere and kind personality, and her specialties are housework and lacrosse. She is not a morning person and tends to oversleep. She possesses the mysterious ability to understand the language of cats. After accidentally saving a black cat (Prince Lune) who darted into the road, she receives a "repayment" from the Kingdom of Cats and wanders into their world. While nearly being turned into a cat herself, she struggles to maintain her sense of self with the help of Baron and Muta.

Name: Hiromi Gender: Female School: Aoi Prefectural High School (2nd Year) A 17-year-old second-year student at Aoi Prefectural High School. She is Haru Yoshioka's best friend and classmate. An active high school girl who belongs to the lacrosse club, she cares deeply for Haru. As the person who knows Haru's daily life best, she is depicted worrying about Haru after she disappears into the Kingdom of Cats. She functions as a supportive friend who stays by Haru's side even when Haru is troubled by her feelings or her future path.

Name: Baron Gender: Male Occupation: Director of the Cat Bureau He takes the form of a bipedal cat baronet dressed in a tuxedo, top hat, and carrying a cane. In "The Cat Returns," he is depicted as a gentlemanly cat who actually moves, speaks, and wields swordsmanship as the director of the "Cat Bureau." This is based on the setting that he is a character in a story written by Shizuku Tsukishima. He is calm, collected, and possesses a demeanor often described as dashingly suave, playing a central role in rescuing the protagonist Haru from the Kingdom of Cats.

Name: Muta Gender: Male Has a criminal record for eating every fish in the Kingdom of Cats. His real name is "Renaldo Moon." He is a large, stout cat and an old companion of Baron. He is foul-mouthed and short-tempered but kind at heart, possessing a side that subtly helps those in trouble. He has lived beyond the lifespan of a normal cat and is depicted as a being capable of traveling between the Kingdom of Cats and the human world. He is a legend for once devouring all the fish in the Kingdom of Cats, and through that connection, he is well-versed in the kingdom's affairs. He is a regular at the "Cat Bureau" and plays an important role in helping Haru and the others.

Name: Lune Gender: Male The Prince of the Kingdom of Cats and son of the Cat King. He is sensible and kind. A beautiful cat with heterochromia, he is in love with the white cat Yuki, and their engagement is depicted toward the end of the story. Haru saving him when he darted into the road is the catalyst for the entire plot. Depicted as having a sincere and gentlemanly personality, he is the one who directly triggered Haru's adventure.

Name: Yuki Gender: Female A white cat with distinctive blue eyes who works as a servant in the castle of the Kingdom of Cats. She is in love with Prince Lune, and their engagement is revealed toward the end of the story. She is a stray cat Haru met in the human world as a child, and Haru once gave her cookies. This past connection serves as the background for why the Kingdom of Cats offers a "repayment" to Haru. Her sad expressions are memorable, and the scene where she reunites with Haru in the story becomes one of the triggers for Haru to regain her confidence.

Name: Natoru Gender: Male The Second Secretary serving the Cat King. He has a carefree and optimistic personality. While he carries out the Cat King's orders, he is also shown panicking when given instructions to blow up a tower. He appears as a pair with the First Secretary Natori, and together they assist the Cat King. He questions Muta, saying he "looks familiar," suggesting a connection to the mass-eating incident Muta caused in the Kingdom of Cats in the past. He plays a comical role that eases the tension of the story.

Name: Natori Gender: Male The First Secretary serving the Cat King. He has a capable and calm personality, acting as the Cat King's close aide alongside the Second Secretary Natoru. Between the two secretaries, he occupies the role of the intellectual strategist. In the original work, three cats with similar patterns appear to surround the Cat King, but he is treated as a distinct entity in the film. He is given a functional role in the story as a character who tries to realistically process the Cat King's whimsical instructions.

Name: The Cat King Gender: Male The King who rules the Kingdom of Cats and father of Prince Lune. He is characterized by his blue and red heterochromatic eyes. He possesses absolute power and has a selfish, willful, and tyrannical side, reigning as the supreme authority of the Kingdom of Cats whose orders are absolute. He invites Haru to the Kingdom of Cats and unilaterally plans to make her the bride of his son, Lune. Accompanied by his two secretaries, Natori and Natoru, he sometimes issues incoherent orders. As a character who combines absurdity with intimidation, he brings both tension and laughter to the story.