Hikari to Yami - Celestial Chronicles

Akeno and Haruto Himejima. Daughter and son of Shuri Himejima and Baraqiel, one of the Cadre's of fallen angel. Inseparable after birth, but separated after a night of tragedy in their eight years old age. The sister one, find a solace and comfort from a High class female devil, Rias Gremory. While the brother one went missing, but ten years later he appeared inside Grigori.