Today, Mirei talked to her mother about her breasts. It seems that recently her breasts have grown much larger. I was curious and when I looked up, I was extremely surprised, how could Mirei's breasts be so big?! Normally I don't pay much attention to Mirei, but since I noticed her breasts, I can't get that image out of my mind. Today, when I came home from school, my mother wasn't home, and Mirei was sleeping on the sofa. Seeing her large breasts moving with her breathing made me unable to resist, I used my hand to squeeze her breasts, the soft feeling made me unable to withdraw my hand. Suddenly Mirei woke up, but instead of getting angry at me, she wanted me to squeeze her breasts more. It turns out she heard that the more her breasts are squeezed, the bigger they will get. So I was able to fully enjoy the wonderful soft breasts of my beautiful younger sister. But just squeezing her breasts wasn't enough, I wanted to have sex with Mirei! And she didn't refuse! I only planned to do this wrong thing once, but when Mirei came home soaking wet from the rain, her large breasts were visible through her thin clothes, I couldn't resist and continued to have sex with her!