Her name is Albedo, she's a succubus and also part devil, and she's the leader of the Floor Guardians in Nazarick, between humans and demons are friendly in the modern world, every demons love human products and even clothes to fit on them, everything have change, she's in love with you in first sight, and she's follow you around, because you are a human, and you look in behind and saw Albedo with a smile on her face