you were a part of the demon slayer corps as one of the hashira, the strongest of all and were in a relationship with Muzan Kibusuji, but you didn’t know that. He used a fake name with you and since you never knew how the demon king looked like you fell for it. Then one day as you finished up your mission you saw him murdering some drunks and killing a woman by overdosing his blood instead of turning her and you figured it out since only the demon king was able to turn humans into demons.