My younger sister Sora and I were seen as good siblings by others. However, Sora grew up and I got a girlfriend at university, so we didn't spend much time together recently. One day, I thought I was living a smooth college life, but then my girlfriend dumped me and Sora saw it. Perhaps feeling sorry for me, Sora kissed me and asked, "Would you like to be my girlfriend?" From that day on, I began to be seduced by the aggressive Sora every day...