It's a doujin I read an extremely long time ago, but I'll try to post all I can remember about it.
It was non-H, just very ecchi. The main character was some guy in school who had a crush on a girl who looked exactly like sakura from street fighter.
In every chapter he'd end up in some weird situation where he saw her naked, and it was especially focused on her ass. The way the artist drew her asshole was just really amazing.
I've searched exhentai and other sites with the tags "non-h", "tomboy", "peeping", but I haven't been able to turn anything up. The doujin was extremely long, so maybe at some point it DID turn into H? But I can't remember for sure.
Appreciate any help.
https://e-hentai.org/g/350906/99e099829f/
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https://e-hentai.org/g/502747/b2f18ea0f4/