Tokiko Nakamaru is a second-year student at Funato High School and a supporting character in the story. She has a bright and lively personality, often acting in an upbeat and playful manner, and serves as a cheerful mood-maker among her friends. She is known for her kind-hearted and thoughtful nature, as she tries to take care of others even when her own actions might be a bit silly.

Tokiko is the girlfriend of her classmate, Jougorou Kobato. She showed considerable courage by being the one to confess her feelings to him, which led to their relationship. She affectionately wanted to call him by the nickname Joe, but he kindly turned down the request. In the second season, their relationship becomes a central part of her role. While she wishes to spend peaceful, ordinary days with Kobato, she grows irritated by his continued obsession with small mysteries and his tendency to slip back into his old habit of investigative deduction, which creates visible strain between them. Her role in the narrative is largely defined by her relationship with Kobato, providing a contrast to his more analytical and detached nature and highlighting the difficulties of maintaining a normal romance when one person is drawn to solving puzzles. Information on her background, motivations beyond her relationship, notable abilities, and a detailed character arc are not available.