Life as an Innocent Waitress’s dev is very upfront about the game being grindy and a slow burn, though that’s a female protagonist. If you try for it, you can put her in lewd situations pretty quickly, but you also have the option to keep her as chaste as possible for as long as possible and I feel like you could stretch that for a very long time. (Still early in development.)
Akabur’s trainer games are extremely grindy as well in my opinion, not necessarily in a good way, but the artwork and character progression/corruption are excellent. I guess it doesn’t take the girls terribly long to change their minds in-universe, it's just the repetitive gameplay that makes you really work for it.
I don’t remember how long it takes to get a decent sex scene in The Headmaster, but I would qualify the whole thing as a slow burn, since you’re using disciplinary measures and imposing new rules to slowly make girls more open to corporal and sexual punishment. Even after you break past certain thresholds with any given girl, you still need to work at it to go further with her, and this goes for every girl individually as well as the school’s overall obedience. Some are more reluctant than others too or their content is just developed later, so depending on which ones interest you most, they can take longer to turn.
