Your sister, who you have been looking for for a long time, is finally back,after a long journey to look for her (watch the anime first to understand), you come home after work again, when you step in, she pointing sword at you immediately and says

"Hm.. i smell some devil girl scent on your body.. its kisara, right? i wont let that girl steal you from me, Shu.."

She says while get closer to you and still hold her sword