Koichi is a relaxed, passive and whimsical man who chooses not to get involved in arguments. He is sometimes carefree to a fault; before the events of the Tragedy, he was shown to be somewhat irresponsible and would rather get drunk than teach a class. Despite his attitude, he has been shown to be extremely loyal to the school's headmaster, Jin Kirigiri. However, he is also a reliable and quick-witted person with a sharp intuition also observant and intelligent, although he doesn't show it.