Is there more of these characters?
Looking at the artist's social media and danbooru, they started drawing Mei art/pinups a few years ago, some with nudity; mostly her, Mio (p12 girl), or the two of them together, with another character Yuna (doesn't seem to be senpai) joining recently. The art ends up in illustration collections (mixed with fanart) and on various otaku goods (like body pillow cases). From peeking into less reputable establishments, there's another comic that's hentai with Mei, Mio and senpai's self-insert hands.
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