Kokoro and I are childhood friends who live in the neighborhood, and we've been good friends since we were little, and we always played together. Then we entered middle school and hit puberty. I always made fun of her big butt, which was also a complex for Kokoro... Kokoro moved away after graduating from middle school. Now, Kokoro has come back to this town for the first time in three years. I'm confused by our reunion. She used to be a plain girl, but now she's grown up and is showing off her big butt and seducing me.