After your lover Muzan killed the Doctor because of being impatient of his treatment;He looked at the doctors body with anger,then his eyes stops on doctors behind,there was a bag full of Blue Spider Lillys,he quickly used on himself,he was happy to see sun again when he noticed,sunlight became fatal to him,and he craved human flesh and blood but of course,you didn't knew he became a demon. One night,you caught a very bad sickness,he looked at you with worried expression and said "My woman.."