Mi-kun is a cyborg cat and the deuteragonist of the Cyborg Kuro-chan series. He was originally a normal kitten whose mother was killed by a vicious rabid dog, leaving him orphaned and drifting until he was found and nursed back to health by the scientist Dr. Go. The two bonded like family. Later, Mi-kun encountered the dog that had killed his mother and was killed himself while trying to avenge her. Dr. Go recovered his body and modified him into a cyborg, bringing him back to life. After avenging his mother, Mi-kun and Dr. Go resumed a homeless but peaceful life, with Dr. Go taking in stray kittens. However, persistent rumors and public ostracization drove Dr. Go to madness and plans for world domination, with Mi-kun at his side as the leader of the Nyan-Nyan Army. Their ambitions were ultimately ended by their rebellious member, Kuro. Accepting defeat, Mi-kun and Dr. Go settled in the Sakuramachi Junkyard with a makeshift home and lab.

Mi-kun is very dedicated and loyal to Dr. Go, their bond remaining firm since they first met. Unlike Kuro, who is rude and violent on the outside, Mi-kun is kind-hearted, noble, and possesses a strong sense of chivalry, despite appearing as a frequent goon. He is a three-star cook but is bad at housecleaning. His primary motivation is his loyalty to Dr. Go, whom he considers family and for whom he would risk anything. His role in the story begins as an antagonist and rival to Kuro, but it evolves over time. He declares Kuro his rival, and their relationship develops from a lethal rivalry into a competitive friendship based on mutual respect.

Throughout the series, Mi-kun undergoes development from a cold killing machine into a character with a conscience who eventually shifts into a more heroic role, often fighting alongside Kuro. His key relationships are with Dr. Go, whom he treats like a father figure and is fiercely protective of, and with Kuro, whose respect he earns over time. In terms of notable abilities, Mi-kun is a cyborg cat modified by Dr. Go and is often depicted wielding a large sword that can heat up. He is highly disciplined and skilled in combat, serving as the effective field commander of the Nyan-Nyan Army. His mechanical body grants him enhanced durability and capabilities, although his appearance is highly mechanical with few traces of his original cat form.