The Bride of the Fallen Angel

When one's mission deviates, a guardian angel will fall into a demon. Yuna was betrayed by her fiancé and the princess she swore to protect, and she was heartbroken and killed. When she fell into hell, she was greeted by a mysterious man, Yami. Yami said that he was her guardian angel, but because her destiny derailed, he was gradually turning into a demon. In order to correct her own destiny, Yuna decided to make a contract with Yami and be reborn as a being named Sher...