Thank you for the feedback!
The game actually has a ton more foreshadowing than you even noticed (for example, everyone's accessories are further hints), so I definitely expected, and kind of wanted people to figure out the plot twist before it was revealed. The main aim of the twist wasn't really supposed to be a "who" situation, but a "how" and "why" situation. I kind of wanted to tell a story where, if you played it a second time and paid attention to the dialog, with the knowledge of what happens at the end, that things would be a lore more clear.
For example, Felix will say something, and he will be immediately shot down. And then Kia will then make the exact same request that Felix did, and be immediately approved. This is why the dialog is so repetitive and it seems like characters just monologue on and on about the same things - because I wanted to really drive across the point that the characters were not in control of their own actions. For example, every time Kia reminds Felix about what they need to do, it isn't just about me dumping exposition, it's about her reinforcing her commands.
As for the final battle... Well, I don't mean to sound rude or anything, really, but... you were kind of playing the game wrong XD (I watched your stream of it)
Each of the characters comes with several skills and/or magic, and I didn't just arbitrarily add them for no reason - every character, and every skill serves a specific purpose in battle, and the game is balanced around you utilizing them to their fullest extent. For example, I don't think you noticed that all of Rose's attacks don't only apply status ailments (which each have a roughly 50% chance of being inflicted), but they also have a 100% chance to inflict a given debuff. So when fighting the final boss, you should be utilizing those debuffs to reduce her magic attack power (since all of her attacks are magic) to prevent her from nuking you with her super move. I also gave Felix his Taunt skill specifically to divert the final boss's confusion and instant death attacks away from the party members who's survival are more important. So... I don't really think the final boss was too hard - I just think you weren't properly utilizing your party member's abilities. :)
Also, I feel like both you and some of the people in your chat felt that the ending was a bit dumb, or even confusing as to why it happened. While I'm not gonna say that you're wrong in your opinion or anything like that... I would like to clarify precisely why I chose that ending. Alathamaskia subjects Felix to a "fate worse than death" - she even says so herself. She does to him what she feels would be the thing he would hate the most. And so... To get back at her, he does the exact same thing to her. He gives her a "fate worse than death", the thing that she would hate the most. So, as someone in your chat had mentioned, it would be morally better for them to just have killed her... but I feel that this was an appropriate end to a character who did some pretty horrific things!
But I definitely do appreciate the feedback! Really! And I hope to make a better game next time!