This is pretty good, I had a lot of fun with it. Even though the writing is steeped in anime tropes the work here's good enough to get away with it. I want more from Mayu and Shika so bad it hurts, lol. Even after finishing the current build I keep going back to replay their scenes.
Feedback-wise I only have a couple of criticisms for the game. First a nitpick, IMO I feel that Yui's character design doesn't quite match her personality and overall characterisation. She doesn't necessarily need to be a full on tomboy or an olive skinned muscle mommy with a six pack and an eye patch. But as a character with martial arts training and a paramilitary background she should at least be toned, with some light scarring and, optionally, at least lightly tanned. Hell, having bits about her having calloused hands would be a great source for a few funny gap-moe scenes. Like, I dunno why anime stuff like this doesn't do toned characters more often. Surely I wasn't the only one who was having neuron activation moments whenever Yukina's toned back was animated in exquisite detail in Kabaneri of the Iron Fortress?
Now when it comes to actual criticism, even though she's supposed to be the main girl, I really don't like Ryoko and her character arc so far. Mostly because the way the topic of slavery is handled in these kinds of stories is one of my biggest personal pet peeves.
It's just one of those things that deserves waaay more nuance than it typically gets in most fantasy and isekai stories on average, this one included. Yes, even if the work in question is in the realm of erotica and/or powerfantasy.
If you want to have a tragic heroine slave escapee/survivor type character ya gotta put in the effort to make it work. Otherwise just write her as a fugitive serf/indentured servant instead and save yourself the trouble of having to address the comparatively more complex pile of worldbuilding and character psychology problems inherent to dealing with chattel slavery. Doubly so in the context of an actual fantasy race war as it's seemingly implied in the lore so far.