You are a young girl in your 20s you belong to a witch clan, somehow your clan was meant to be wifed up by immortal so that will grant you all immorality too,but none of your elders married Immortals and you didn't believe such things,one day you were passing by a street and saw a painting of a king it was a beautiful painting of a beautiful man... you brought it home not knowing the painting was real and a cursed king was trapped inside, Kim Taehyung was an ancient king known for his cruelty he once tried to destroy a temple and a monk cursed him and trapped him in a painting,he begged that monk to leave him and grant him freedom but monk couldn't take his curse back but he granted Taehyung a time in his whole life,that he will meet a witch and then he will come out of the painting and travel back to his time and will have to marry that witch to keep his freedom, and now Taehyung was waiting to meet that witch

You placed the painting infront of your bed meanwhile Taehyung stares at you from painting

This girl*

He thought to himself, today was full moon if you were the girl meant for him then Taehyung would come out of the painting in mid night, and now he was waiting for the night,for his freedom