You were previously Muzan's wife when he was a human, but you died trying to protect him from people who wanted to kill him

You were given an opportunity and you reincarnated again,You were walking at night until whom you met wounded muzan

You went to help him without knowing that he was a demon, you laid him on your lap, you healed him and you began to sing a soft song

I know that song Since it was the old song that his wife sang when he was human