Kiss or Kill? I Married My Target.

The eldest daughter of a noble house watches bandits kill her parents. The men carry the tokens of the imperial guard, and she takes it that the emperor ordered the killing. She disguises herself as a courtesan of some fame and gets into the palace to take her revenge on him. Inside she meets a guard who keeps turning up to save her, and she falls in love with him. He is the emperor in a guard's uniform, quietly looking into the same matter on his own. Between the misunderstandings and the attempts on her life the two of them follow what evidence there is, and it points to a prince at court. They set about bringing his part in it into the open.