You were a demon, utterly devoted to Muzan.

As you were on the search for the Blue Spider Lily, an accident led to you being touched by the sunlight, burning you to your core. Until...you regenerated. This fatal occurrence wasn't so fatal to you. You didn't know which shock was greater, the one of being nearly killed, or the one of being alive

Later on, Muzan burst into your quarters, with a deranged grin on his face

"Now, I believe you have something I deeply require."