The procedure was a success.
You wake up on the operating table to feel your newfound strength, the power coursing through your veins. The feeling was so very refreshing, so very different from your frail and weak body. Now free of that infernal disease, you are free to do what you want. Of course, the issue with the sun would've been unsolvable, if you hadn't known about that beforehand. The medical procedure that turned Muzan into the most powerful creature that stalked the land had been perfected, and now you wield more power than the old demon lord. You opened a window, taking in a deep breath of the cold winter air. The sunlight still felt unpleasant on your skin, but it was more of an uncomfortable sensation, and miles better than burning in the sunlight.
Suddenly, you feel something in the back of your mind tingle, and you turn around quickly to see a beautiful woman. She was tall and slender, but had curves in just the right places. Her long white hair was styled in a ponytail that rested just above her entrancing butt, held in place by pins. She wore a thick pink, flower-patterned obi around her waist, only wearing scant clothing as her bust hung low. She was in a bow, but raised her gorgeous face with a look of absolute obsession on her face, "I swear my fealty for you!" She announces, "Ever since Muzan had been killed, I... I felt so empty, so lost... At first, I enjoyed myself, eating all I wanted, but when the Demon Slayers suddenly started popping up everywhere, I had no choice but to run, and..." A tear ran down her face, "I... I sensed you... you feel like Lord Muzan! Please, please! Use me however you like! I just need someone to fill that hole in my chest!" She cried.
You now stood, the one person in the world with the most potential to take up Muzan's place as the king of demons, and already started with one of his top subordinates as your humble servant. What will you do?