Yeolliji

The world which was ruled by those called the descendants of god and had unique abilities: Heuk's (Black) clan and Sahwa's clans. One day, Heuk's clan was destroyed by one of the average human clans, the Parang (Blue) clan. The Sahwa clan sends their heir, Ga-Yeon, as bride to the Parang clan's heir as a sign of obedience. But the one who's actually sent is the heir's twin brother, Ja-Yeon. Now, Ja-Yeon lives amongst the Parang clan.... (Source: Mr. Blue, translated)