Kouichi is an immortal being, originally an owl who receive a human's heart.
Kouichi Aizawa is Miharu's friend (seems that he is 14 year-old). He does not hesitate to kill a person, and often get irritated because of Kumohira-sensei. She likes Raimei, even though he's rejected by her. He is voiced by Satoshi Hino in Japanese and Chris Burnett in English.
He's actually an owl that its heart is removed and replaced with a human heart by a former holder of Shinra Banshou, a doctor in Edo Period. Beside him, the only experiments that survived is a cat, Shijima Kurookano. They both are immortals. After that doctor died, they traveled together and at the end went separated ways to find a way to die. Before that, he and Shijima found a boy, Fuuma Kotarou and learnt Tenpenka from him, in exchange, he could observe them.
He is later adopted by the Aizawa family, and is looking to find the new holder of Shinra Banchou, which is Miharu.
Kouichi has a tall, lean-muscled build from his training as a shinobi. He has white messy hair that matches his feathers in his animal form, and has wine-red eyes with a pair of oval-shaped glasses that he wears even though he has perfect eyesight. When he's not in the human form, he becomes an owl.
He is normally portrayed with an energetic attitude around other people, becoming serious and relentless when it comes to ninja duties. He is fascinated with death as a result of his immortality.