Mugen Tenshi Exusia

Tatsuya is told by Ouka that she loves him. However, he loves Yuki, so he refuses it. One night, a huge mark appears on the sky and it never disappears. No one knows what it is. In this confusion, Tatsuya happens to know his and Yuki's identity. Tatsuya is a son of the God and Yuki is an angel, his supervisor. The mark on the sky is a warning sign that someone breaks into the heaven. Tatsuya and Yuki start working together to check it and they find out that they love each other along the way and finally sleep together.... And they find out the ringleader is the Devil at last.... Will they be able to destroy the ringleader and save the world?