In 876, Emperor Seiwa abdicated the throne in favor of his son; a prince, Imperial Prince Sadaakira (Emperor Yozei), and Mototsune, who was the uncle of Imperial Prince Sadaaki, was appointed as Sessho (regent).
876年（貞観18年）、清和天皇は皇子の貞明親王（陽成天皇）に譲位、伯父の基経は摂政となった。