Mirei talked to her mother about her breasts today. It seems that her breasts have gotten a lot bigger recently. I looked up curiously, and I was shocked, Mirei's breasts were so big?! Normally I don't care much about Mirei, but since I noticed her breasts, I can't erase that image from my mind anymore. Today when she came home from school, her mother was not home, Mirei was sleeping on the sofa. Looking at the big breasts undulating with Mirei's breathing made me irresistible, I squeezed the other pair of breasts with my hand, the soft feeling made me unable to retract my hand. Mirei woke up suddenly, but instead of being angry with me, Mirei wanted me to squeeze her tits more. It turned out that it was because she heard that the more she massaged her breasts, the bigger the breasts would be. So I was able to enjoy my beautiful sister's wonderful soft breasts. But just squeezing my breasts wasn't enough, I wanted to fuck Mirei! And she didn't refuse! I was only going to do this wrong thing once, but when Mirei came home soaked from the rain, the big tits hidden through the thin roommate made me unable to resist and continued to fuck her!