My childhood friend's younger sister is dating me. Actually, I've always liked my older sister. I'm so jealous that I went so far as to undress and seduce Yumeno Aika. (SONE-640)

If we had been honest with each other sooner, we wouldn't have hurt anyone... Aika (the older sister), Lisa (the younger sister), and I were childhood friends; we were always together throughout our school years. I liked Aika, and I was sure she liked me too. But because our relationship was so close, things never progressed, until I turned 30.