The fact that I'm willing to both play something like this and admit it shouldn't surprise anyone. I mean, I freely admit to playing a lot of RPG Maker and Wolf RPG Editor eroge, this thing's significantly more mundane than a lot of those games get.
Anyway, this is a very standard cheesecake game from qureate, the company that once got in hot water for naming all the characters in a different game of theirs that includes something called an NTR mode after members of an idol group (because apparently they didn't have enough common sense to know how that was gonna go). This is not that game, it's a completely different horny-but-not-R18 qureate game. The plot of this one is that the Demon King has kidnapped the princesses of the continent's two biggest kingdoms and locked them up in a castle. To make matters worse, the hero who's supposed to be able to save the day is dead. Except he's able to help the princesses escape as a ghost, which lets them avoid having to draw a male character while still having one. There's only three characters who actually appear in the game: the cheerful and airheaded Princess Aria, the ISO standard tsundere Princess Zena, and the pervy but ultimately kindhearted hero.
This is not a game you play for its deep characters or engaging story, is what I'm saying here. It gets the job done, and that's pretty much it.
The actual game part is a room escape-type graphical adventure game. You go around solving puzzles, collecting items, and all that good stuff. The main conceit is that, since you're playing as the hero who can't interact with anything, it's the girls who are actually manipulating stuff in the game world. Which means they're visible interacting with everything you point out and providing ludicrous amounts of panty shots in the process. That's the game's main selling point, even, that you're constantly being distracted by two cute girls while you're trying to figure things out. It's a remarkably honest way of selling the game in that regard.
There's also several timed puzzles that put the girls in highly suggestive positions (complete with animation!), and these are actually pretty important because they're where you manipulate affection levels. Basically, running out of time or, uh, interacting with the girls causes their affection levels to go down, while just solving the puzzles raises them. It's honestly a pretty bizarre way to go about it since it means going for a particular character ending requires you to show more interest in the character you're not going for, but given the context it makes sense. The puzzles themselves are mostly simple enough, with the noted exception of the FUCKING LIGHTS OUT PUZZLE SERIOUSLY WHY THE FUCK IS THIS BULLSHIT SO FUCKING COMMON-
Uh, anyway. What really stands out to me about this setup is the fact that this isn't an eroge. The premise is extremely horny in a very particular way, there's plenty of situations that feel like they could've easily been turned into full-on H-scenes, qureate isn't exactly shy about going in that direction, and yet...there's no R18 version of Prison Princess. Even the PC version that's sold on eroge sites isn't any different. I just don't understand what they were going for with that.
There's also the issue of localization quality. As usual, qureate trusted Medibang to put out an English version for them, and as usual Medibang dropped the ball. I've seen significantly worse from them in other games, but this is still a game that, among other things, gets the green/blue thing wrong literally every time it comes up, and at one point refers to a carpet as a bed. And in an adventure game where language needs to be precise to help you solve the puzzles, that's just plain unacceptable.
Overall, just a mediocre game. I can see it holding some amount of interest if you're really desperate for something horny and don't know where to look for anything more effective in that regard, but otherwise it's kinda just there