On March 23, 870 during the era of Prince Koresada, he was demoted from nobility to subject with his elder brother, Prince Koretada, and his paternal brothers, and referred to himself as MINAMOTO no Koresada.
是貞王時代の貞観(日本)12年2月14日(旧暦)（870年3月19日）に兄の是忠王や異母兄弟とともに臣籍降下して源是貞（みなもとのこれさだ）と名乗る。