Ōku was a Japanese princess during the Asuka period in Japanese history. She was the daughter of Emperor Tenmu and sister of Prince Ōtsu. As a young girl, she witnessed the Jinshin War. According to the Man'yōshū, she became the first Saiō to serve at Ise Grand Shrine. After the death of her brother Prince Ōtsu in 686, she returned from Ise to Yamato to enshrine his remains on Mt. Futakami, before a quiet end to her life at age 40.