Koito is a blind shamisen player serving the Shunra-tei theater group. Her lack of sight sharpens her remaining senses, especially her hearing and sense of smell. She typically wears a traditional kimono and keeps her dark brown hair styled in a bun, with strands covering her right eye; her blindness means her eyes are usually closed.

She trained under the shamisen master Otome until Otome fell ill. Koito holds deep respect for her master but wrestles with self-doubt, fearing she may never match Otome's skill, particularly on complex pieces like "Tsujiurajaya" ("Fortune Tea House"), which demands perfect coordination with the storyteller.

Koito forms a significant bond with Mameda, a tanuki girl training to be a rakugo performer. Her heightened senses allow her to detect Mameda's true nature early, recognizing both the distinctive mountain scent and behavioral traits. She chooses to keep this secret, knowing Bunko, the rakugo master, would stop Mameda's training if she knew. In exchange for her silence, Koito gains permission to touch Mameda's tail, finding comfort and enjoyment in fondling it.

Her role leads to a pivotal incident during a "Tsujiurajaya" performance with Bunko. Koito accidentally falls, spraining her ankle and damaging her shamisen. Facing cancellation, Mameda transforms into a shamisen as a replacement. Koito plays this transformed instrument, allowing the performance to proceed. Mameda's occasional vocal interruptions force Bunko to improvise comedic lines. This incident reveals to Bunko that Koito knew Mameda's secret, yet Bunko continues teaching Koito, trusting her discretion.

Within the Shunra-tei, Koito maintains respectful relationships. She interacts cordially with Omatsu and holds Bunko in high regard, unaware Bunko is secretly a kitsune. Her interactions reflect a gentle, caring demeanor, marked by loyalty to colleagues and a commitment to supporting rakugo performances through her music.