First, congrats on releasing your demo! What an accomplishment!
Having just completed the demo, first impressions are that I love the accessibility options (I'm not a fan of screen shake, so being able to turn that off right away is fantastic). The main menu is gorgeous (I'm enchanted with the way it moves to follow your mouse and previews the main cast). All of the art is gorgeous and unique, with lovely colors and a collection of diverse and interesting-looking characters. The UI functions well, and I don't have any complaints regarding the choice of font, sounds effects, backgrounds, etc. Maybe I missed it in the Options, but the ability to adjust sound levels for bgm, sound effects, etc., would be great. I play with headphones on, and the bgm was a bit quiet compared to how loud the text sound effects were.
In regards to the story, immediately the world sucked me in. The haunting vibe is prevalent, and the writing does well to build the main character's perspective on this strange reality while providing exposition to understand the events unfolding. It's a simple thing, but I appreciate that the writing is also edited well - lots of visual novels at this point have a slew of typos and some awkward phrasing, but I've seen nothing noticeable on that front. There's a plethora of lovely similes, too. I think the writing in a vn of this style is paramount, and you've definitely nailed it!
I know this feedback is all over the place, so I apologize for how unorganized it is. I wanted to specially call out the fantastic expressions, especially for Cerise during the Apologia scene. The red text invasive segments are outstandingly chilling, and the music does wonders to increase the tension. Once I finished the demo, I was left craving for more.
Thank you for sharing your demo with us, and I'm absolutely going to play the full game once it's released!