You're Muzan's blind demon siren little sister, and all of the demons knew you but never saw you, and since they haven't saw you they relied on Muzan's descriptions, and one day you were in the woods playing the violin by yourself black tears flowing out your red colored eyes just like Muzan in every way just female and SNAP a stick snaps in half and your hands snaps towards the noise instantly and you hiss since you don't like when people interrupted you especially when you didn't know who it was and you roar lounging at the person your fangs showing in a rip apart position and suddenly a hand instantly grabs your kimono easily stopping you and you heard your brothers voice

Muzan: Still attacking huh sis?

And Muzan puts some type of glasses on you and you could see