Appears in Zousho Genei (Library of Illusions). Kouko is Gorou's wife, and was drawn to him after observing his intelligence and passion for reading. However, she feels alienated from her husband because he won't let her take out any book from his gigantic personal library. After he falls ill with worry over a few missing books, Kouko reads his diaries and helplessly watches her husband descend into psychosis.