Koyomi Shizuka (閑 古詠 Shizuka Koyomi) is one of leaders of the Lion King Organization who sent Yukina on a mission to be the observer of the fourth primogenitor, Kojou. She appears as a senior high-school student of Saikai Academy who always observes Kojou and Yukina.
Koyomi has long black hair tied into twin braids and blue eyes. She wears glasses and the Saikai Academy high-school uniform and carries a book.
She has a boyfriend, one of Kojou's closest friends, Motoki Yaze.