自购https://www.dmm.co.jp/dc/doujin/-/detail/=/cid=d_607698/
中文区的广告汉化组勿扰。
COMIC1☆25発行「妹の友達がいちばん気持ちいい」とCOMIC1☆26発行「妹の友達がいちばん気持ちいい2」の合本です。

why do the nipples look so photoshopped and blurry

Base +31

https://www.melonbooks.co.jp/detail/detail.php?product_id=2597040

[Synopsis]

A sweet and dangerous study session begins between the protagonist, a university student and his sister's friend, Yume.
As they spend time together to help Yume with her studies, the two gradually become closer.
At first, it was just a study session but the moment her sister leaves, the feelings hidden deep in Yume's heart gradually surface.
Yume shows an innocent smile as she is noticed for the first time for her charm and behind that lies hidden excitement.
Alone in the house, she becomes bolder, one step at a time.
"Is it okay if I touch you just a little?"
A sweet and dangerous time unfolds while her sister is away and the new feelings she has for the protagonist explode.
The study session gradually turns into "reward sex" and the relationship between the two progresses to a deep pleasure.
Enjoy the sight of Yume, who is completely out of control despite her pure appearance!

Base +28, AriSapes +8, Miosan389 +6, nuts987 +13