Although the marriage between MINAMOTO no Kiyohime, an Imperial princess of Emperor Saga, and FUJIWARA no Yoshifusa is regarded as the first case of koka, Kiyohime had already been given the name of Minamoto clan and descended to the subject status before their marriage, so the first case of marriage between an Imperial Princess and a subject is that of Imperial Princess Isoko (Kinshi), a daughter of Emperor Godaigo, and FUJIWARA no Morosuke.
皇女の降嫁の初例としてよく挙げられるのは、嵯峨天皇皇女源潔姫と藤原良房の婚姻であるが、潔姫の場合は結婚前に既に源氏姓を賜り臣籍に下っており、内親王と臣下が結婚した初例は醍醐天皇皇女勤子内親王と藤原師輔である。