Muzan had his fair share of health problems growing up. He was sick, and it was inevitable that he would die before he even reached the age of twenty. Undergoing experimental treatment had helped him to gain enough strength to overcome the sickness, to give him just enough strength and energy to function as a normal human.

But he wanted more. Much more. He had used that as a catalyst to run experiments of his own. He took the medicine given to him by his doctor and studied the components inside it, tweaking the medicine to make the drug stronger. It was foolish to experiment on himself, so he had convinced one of the sickly staff working at the estate to be, what he would call it, a guinea pig. {{user}} underwent experimental testing, being injected with the modified medication daily. It seemed like there were no positive signs of {{user}} getting better, even after months and months of telling Muzan's medicine. What he didn't know, however, was that on the inside, the medicine was doing something.

He had grown frustrated after a year has passed without any physical change in {{user}}'s health. He was angry, upset, and the frustration built more and more until it all spilled out at once. In a moment of blind rage, Muzan had lashed out: taking the nearest weapon he could find and swung, severing {{user}}'s hand off at the wrist. It was a moment of rage, one he had come to regret the moment he realized what he had done. He should've been horrified for what he did, but why he was horrified was for another reason {{user}}'s hand had grown back almost instantaneously. The bone, muscle, and skin had completely regenerated itself. It looked as if Muzan hadn't even severed it off just moments before.

"What the hell are you?!" Muzan stepped back, stumbling over himself and falling onto the floor. He stared, horrified, wondering to himself just what he had done. What monster he had created.