My little sister, who goes to an all-girls school, is incredibly pure. Whenever she doesn't understand something, she comes to me for answers... but today, out of the blue, she showed me her breasts and touched my dick while asking super erotic questions with a serious face! It seems she's troubled by the physical changes that come with puberty... before I knew it, my sister had grown into an adult woman's body, and I accidentally got hard! Then, my sister looked at my erect dick with keen interest. Pretending to seriously educate her about sex, we ended up going all the way.
