Yurika is shy, quiet, and gentle, but she only warms up to me. Our parents don't notice, but Yurika actually has a strong curiosity about sex, and I've been sexually teasing my sister since we were kids. One day, our parents go back to their hometown because of an injury to our grandfather, but my sister doesn't want to go with them. She gives up on making her come along and calls me over to stay alone.
