I like the fast speed in getting to
some form of "action," especially that "action" being a futa jerking off (very hot, criminally underused around here) but the opening also feels a little... rushed, maybe? What happens in the course of one morning feels like something that'd take at least a few days to go through in a different game. Like, Milly finds out she's out of her libido-suppressant pills (permanently?), just decides she's fine with that, immediately starts getting horny for her "mom" figure and jerks off for the first time ever (despite having built up 10 years' worth of a porn folder), then she meets her not-brother's friend and goes "yeah, I'm gonna fuck her."
The whole "life changes completely in one morning" scenario feels like it's better-suited to more extraordinary/fantastical circumstances (getting isekai'd, some dormant power being awoken, arrival of a supernatural entity, etc.) but here it's just kinda like "oh a girl with a dick wakes up, circumstances finally allow herself to get horny after years of chastity, and thus she swiftly turns to cucking people." (Though I'm also glad this
doesn't have any kind of extraordinary/fantastical circumstances set-up.)
I wouldn't even call it bad writing or anything, though? Everything that happens at least makes some kind of consistent sense, but so much of the set-up feels like it's depending on a comparison to a "Milly before her pills ran out" that we've just never seen. (A similar sentiment to what
bob_the_builder said right above me here.)
All that being said, I'm looking forward to more. I like what you've done with the Koikatsu models (especially after playing some painfully-bland-looking Koikatsu games recently) and I'm definitely keeping an eye out for the futa-on-futa content (another thing I feel is underused around here).