I liked the story.
You've presented each character that appears in each setting very well, and even though everything takes place in the world of Echo, you don't get too attached to the characters of themselves. You try to tell a new story based on it, which perfectly adds a fresh air.
I've seen one FVN that tries to apply the same formula arounds the world of Echo, but it doesn't have the same execution as the one I'm seeing in this game, since I think it focused more on the CG than the writing in general.
And here's my other point.
The writing and CGs: While the game lacks of CGs, it doesn't really need it since the plot itself is already interesting, especially with the backstory of the two protagonists, the mystery surrounding it, and many things I'd like to say but might be a spoiler for people who haven't played it yet.
The plot is also moving along well, with a sense of drama, mystery, and as is typical the suspense or psychological horror.
Regarding the sprites and music: The music is fine, but in the sprites there's a problem. The type of drawing that is being applied looks adequate with everything that is being told (such as astronomy or mysticism), but there are times where it cannot be displayed correctly due to the backgrounds, so one of the solutions that I could suggest is to give a dark fill to the sprites or a way to make them look correct in the scenarios. (although well, I know that they are possibly temporary sprites and you want to change the style but it is worth giving a suggestion here, hehe)
In short: Great work presenting your story. You still need to improve certain visual aspects, as I mentioned with the sprites, and possibly give the protagonist more backstory, since I still don't understand his "power" or how he obtained it.
P.S. I was surprised to hear about your game, as it's pretty under the radar and isn't in the FVN database. I recommend registering your game there, and you might get more visibility when you upload an update to your visual novel.
I also recommend again exporting your games to other platforms like Mac, Linux, and Android. Relying on a single platform limits the number of users who want to try your project and don't have a computer or have another operating system.