I generally don't bother throwing out too many thoughts on games that are "in progress", but since the dev is actually paying attention to this thread, I figure I might as well lay out some thoughts here before I leave the game on ye old watch list for another year or two or until it gets completed. Depends. So many games, so little time for them all, and even less money...
Still, corruption is a fetish that is near and dear to my heart, so I'm somewhat more invested here than in other projects I've seen around.
Which is why, to start with, I'll talk about said corruption. I like the fact that it's actually corruption, and not just slutification. While pleasure is the method used to break the girls, it's not just pleasure, and the end result is not just useless sluts, but utterly insane individuals who are willing to do anything and everything for their Master. Furthermore, the fact that all the girls so far have some elements of their initial inclinations remaining as part of their twisted personality makes it all the better. It's most obvious with Yukako, but the others have enough divergence to them to keep them interesting in their corrupt forms.
I especially like the fact that the MC HAS to give them that one, true moment of choice. It's what switches this firmly into actual corruption, and not just mind-control/brainwashing/identity-death/whatever, which are fun too, but they're their own things, and not specifically corruption. At best they can be considered subsets of it. A lot of games and stories fail to grasp that essential element, the fact that true corruption comes from one's own choice, not from coercion or manipulation of any kind.
Those are the really good things so far.
However, there are also so "not so good" things to take into account as well. The biggest problem that's starting to crop up in the game quite a bit is the same-iness of the corruption steps. All the girls go through Strip, then Blowjob, then Sex, then a bit more Sex, then transformation. While the individual aspects of the girls helps alleviate things a bit, since the details that break them and their circumstances are a different and whatnot, the steps, especially for the smut, are extremely similar. The positions are often very similar as well, which makes things even worse, and even animations aren't gonna do much about this problem.
The sex scenes absolutely need more variation, otherwise, people will quickly reach the point where they just skip them. There being bunches of girls is NOT a replacement for variety in the smut. Add some more boobjobs in different positions. Add some actual face-fucking. Hell, add some anal. Especially for the threesomes, the girls have tails, make use of that. Even something as simple as one of the girls groping her own boobs while she rides cowgirl can chance the visuals and the feeling of a scene a lot.
I don't know what the exact limits are for Koikatsu stuff, but based on other projects I've seen using it, I'm pretty sure that what's currently in the game is nowhere near the limit.
When it comes to other things, it's more nitpickiness on my part than anything else. Like the fact that MC remains human looking after taking the power of the Dark Lord. If his corrupted victims becomes demons, it's EXTREMELY weird that the MC remains as human as he is when he gets a much worse dose of things and keeps growing in power. Personally, I've never been one for the bland self-insert MC, and prefer MCs with personality. I'm also fond of non-human MCs too, so if this MC become more monstrous, or at least got his own set of wings, tail and horns, I'd like things a lot more.
Can't really comment too fairly on the gameplay. There's not much of it, and the majority is pretty generic RPGM stuff without any real flavor thrown into it. It's definitely one of the weaker parts of the game for the moment, made all the weaker by the fact that even having a gear tab seems to be blatantly pointless at the moment.
By the way, why the heck does Yukako, the priestess and thus magic user of the party... have less MP than Rina, the knight who has literally only ONE spell at the moment, which you're not likely to use anyway because her M.Atk stat is garbage? Is that a bug or is there some kind of reason for it?
If I'm to suggest something, it'd be at least being more creative with the skills, their names, their effects, their descriptions. As well as ensuring that everyone has at least some options to spend both TP and MP, and not just one or the other. As things currently stat, outside of Rina, everyone's TP bar is pretty damn useless. Maybe that's planned for further into the game, but right now, it feels weird.
This is made worse by the fact that it feels like the default miss chance is pretty high, which makes skills like double-strike extremely useless on top of the fact that they hit like a wet noodle when compared to magic. Well, to be fair, most of Rina's skills feel like they hit like a wet noodle anyway... barely adding much damage over her auto-attack.
Still, balancing is a long-term goal. I figure things are gonna change in various ways as the game moves forward. For me, I didn't feel like the team was under threat at any point in the game, not even the big boss fight. Didn't even need consumables. That said, this is partly because I've played a LOT of RPGM games to the point where I've turned "not using consumables if at all possible" into an artform...
Well, anyway, while there's more I could probably nitpick about, I think this is enough for now.