My little sister is getting cuter and cuter, and it's a problem. I thought she was just a kid until recently, but now that she's a high school student, she's super cute, and her breasts are getting bigger, so I can't stand it as a virgin!! What's more, when my Kokoro-hearted sister finds out that I'm still a virgin and I can't stand to do naughty things, she does something!! What a surprise!! "If you want to do something naughty, you can use my body, big brother. It will be a good practice for me..." she said!! So I took her up on her offer...