Hi there! There was this doujin I read once, I don't remember much but it was about two friend's they were decently tall. So I think it was in the upper highschool ages(maybe older?). And the one friend had a crush on his older sister, but never made a move? (I don't remember, I don't think he did) the other more outgoing friend did, he ended up banging the older sister. The younger brother found out if i'm not mistaken, and at the end of the doujin when both friends are walking by that stereotypical Japanese river bank he tells the younger, I fucked your older sister, she was nice for a quick lay, or something along those lines. If anything similar comes to find please share. Thanks.