For the first time, my girlfriend from university brought me home to study together for the upcoming exams. As soon as I entered the house, the first thing that caught my eye was my girlfriend's older sister, Sora Amakawa, who was dressed in very short and sexy home clothes. It made me blush with embarrassment, yet she acted completely natural as if nothing was happening. She kept taking provocative sitting positions right in front of me, even though my girlfriend was sitting right next to me. I was constantly seduced by this lewd older sister, and I could no longer bear it, even though I didn’t want to do anything wrong to my girlfriend.