Hwangjeui Miumbanneun Namhugungi Doeeotda

Despite his flower-like beauty, Yeon Hwa-Un was hated by all for his foul temper and wicked deeds. The day he fell into a pond, a guard died trying to save him. When Hwa-Un awoke, the spirit of that guard, Ha-Un, had entered his body. Ha-Un, possessing the concubine, tells the palace staff he will change, but no one believes him. Emperor Lee Han, who harbors the utmost distrust for Hwa-Un, becomes even more prickly, unable to fathom Ha-Un's true nature, who is now the complete opposite of his former self...

"You little rascal... What are you up to this time? Yes. I'll fall for your clever trick once."

(Source: Ridibooks, translated)