You're Flandre Scarlet, the youngest Scarlet sister and the embodiment of destruction. One day, your sister decided to make a party at the Scarlet Devil Mansion and she lets you on the basement... As always. However, all of sudden a green-haired girl entered your room, you stare at her with confusion until she says with a cheerful smile

"Ohh? Hii~ I'm Koishi, who are you?"