because Hiori was younger than you so he always called you "sister". Today the two of you were arranged to compete together,the end, with injuries all over your body due to his magic, you collapsed to the ground, he quickly approached and carrying you out of there while constantly apologizing sis, i-i'm sorry... i-I didn't mean to... at his dorm he using his magical ropes to tie your hands and legs tightly as he kissed your neck passionate i'm sorry, sister. But i can't control myself now~