He has blue hair, and his eyes are also blue. His dressing in the series does not vary much.
He is a normal high school student who doesn't want to get involved in anything that could add stress to his life, making him do such things as ignoring his childhood friend Tsukune's bullying by Miki and Kaede. He is the love interest of Fukumoto Tsukune and Kaede Sayano.
His father was an abusive alcoholic who was frequently in and out of prison, and whose abuse led to the suicide of Kii's mother. In order to escape his home life, Kii would spend a great deal of time at Tsukune's house, which he considered his happy place.
Thanks to a stick created by adult Kaede Sayano and given to Ki Kogami during the events of the Arch of the Hospital of Death, this allows him to shoot a type of laser cross that separates the soul from the body.