Yaksogeul Han Geon Naega Aniya

"Kill me, as you promised."
When her twin sister Leyla, the Holy Maiden, suddenly disappears one day, the ordinary Elena finds herself having to marry Crown Prince Kyle, a man infamous for his ruthlessness, in her stead. After a dreadful marriage ceremony, Kyle demands that a certain promise be fulfilled, to Elena’s confusion.
(Source: Manta)