I have two sisters who are childhood friends. The older sister is in the same grade as me, and the younger sister is three years younger. When we were little, we often played together, but as we got older, the opportunities to see the younger sister, Mirei, decreased. The older sister confessed her feelings to me and we decided to go out. I went to Mirei's house to tell her, but... What... Isn't she in a congratulatory mood? Her face was twitching. Is it because she felt like her older sister had been taken away from her? ーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーーI was invited to her house again, and when I visited... What!? Oh, her breasts are about to overflow!? "Hey, Mirei, what's with that outfit!" "Huh? Aren't you cute? It's fine, it's Mirei's house after all." Mirei appeared wearing a very revealing outfit, and with her arms folded, she pressed her breasts against me. It was so obvious that I couldn't look at her directly... I see, Mirei liked me! That's why she had that suspicious look on her face. Even though her sister was nearby, she was flaunting her cleavage and pressing her breasts against me in an attempt to seduce me. I had no idea that she had such outrageously precocious breasts... She even gave me a titjob when she wasn't looking... At first I accepted it on a whim, but Mirei's seduction only escalated... She straddled me while my girlfriend was passed out drunk and had an affair with me... This is bad, this is bad! But I didn't dislike this thrill. Even though I knew I was betraying her, sex with Mirei was so pleasurable that I couldn't stop.