Empress Kōgyoku
642: Kōgyoku became empress but stepped down after Soga no Iruka's assassination. 645: Kōgyoku abdicated to her brother, Emperor Kōtoku.  654: Emperor Kōtoku died and the throne was empty.  655: Kōgyoku became empress again, now known as Saimei.  661: Saimei died and the throne was vacant again.