Ennei was born as the first son of Eijun OTANI, who was the eleventh son of Koei OTANI (Gennyo), the twenty-second chief priest of Higashi Hongan-ji Temple, and served as Kagiyaku and the chief priest of Hakodate Betsuin.
東本願寺第二十二代法主・大谷光瑩（現如）の十一男で鍵役や函館別院住職を務めた大谷瑩潤の長男として生まれる。