Kosihiro Daimon, nicknamed "Little Daimon," is a 36-year-old police officer and one of a pair of identical twins, alongside his elder brother Kenshiro. Both brothers share a family background fostering mutual distrust of taxi drivers, especially Hiroshi Odokawa. Due to Odokawa's visual agnosia, Koshiro appears as a meerkat to him, though his human form is documented as his true appearance. Koshiro possesses a naturally talkative and somewhat absent-minded personality, described by Odokawa as unintelligent. He holds a strong sense of justice and initially displays unwavering, naive trust in his elder brother Kenshiro. His straightforward motivation for becoming a police officer is to punish criminals, and he is a fan of Taichi Kabasawa.

When presented with evidence of Kenshiro's corruption by Odokawa, who sought Koshiro's help arresting the yakuza Dobu, Koshiro confronts the moral compromise his brother represents. He makes the pivotal decision to personally arrest Kenshiro, moving beyond his naive reliance on his brother's authority towards independent moral judgment based on evidence, acknowledging a reality more complex than his initial black-and-white view. His sense of justice remains a key motivator, making him cooperative when requests align with fighting evil.

In the film *Odd Taxi: In the Woods*, which reconstructs and extends events beyond the series, Koshiro continues his police duties. The film's expanded ending, confirming Sakura Wadagaki's arrest for her crimes, implies Koshiro's ongoing involvement in resolving the case.