For my feedback, I can't evade mentioning anything without spoiling the story, so...
!!! Spoiler Alert !!!
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Firstly, it's good that you have the disclaimers at the start regarding sensitive topics.
I find the first when where Vega spends too much time in their room and house. It feels like the pacing is too slow for me. But due to the overthinking native, it has a narrative cohesion. Honestly, there was just too much monologue for my taste. But to each their own. I would look into trimming some monologue that doesn't really serve a narrative purpose. Since you're hinting that something big is happening on the fourth day at the beginning, I was looking forward to what transpired until that time. The pace only picks up when we're at the Abandoned Church.
Vega mentioned that they wasted most of their twenties rotting inside the room. From It feels more like Vega is still a teenager or just early twenties. The dialog and how the group also sounds more like teenagers instead of fully grown-adults. From my experience, by late twenties most people would be already too busy with lives instead of visiting your basement to practice band. Unless they're really passionate about music, and even if that is the case, taking break from a whole month will not work well for your music career. But who knows, maybe the characters in the story are already somewhat successful in their career to afford the break. These are the discrepancies that I'm struggling to reconcile in my head while playing.
Some comments on the UI...
In the selection UI (e.g. in the Abandoned Church when choosing to go to the Sun Room or Graveyard), I find it unusual that the border also expands vertically when you hover on the option. It must be that the size of the border scale together with the size of text, and when the text get slightly bigger when you hover them, the border also get bigger.
The UI at the bottom of the screen is decent enough to not be cluttering the space. It would probably be a bit better if the options can automatically hide itself when your mouse cursor is not hovering them. I am saying this because the dialog window is also at the bottom half of screen, so hiding the UI when you're not hovering them will put more focus on the dialog window for better immersion. The last option only says "sett", while it's easy to know that it's settings, why not just show the full word?
The rhythm mini-game at the end is such a fresh break from all the dialog! I was playing on PC with a keyboard. It may be worth trying with using different keys for the inputs as opposed to the arrow keys. Since the character is playing a bass with vertical four buttons, maybe using key layouts of the following (using right hand) would be worth experimenting:
"space-bar" -> thumb
"N" key - index finger
"J" key - middle finger
"I"key - ring finger
I think this will align thematically more with the layout of the game and bass instrument.
The rhythm and button timing seems a little bit off for me, but since it is not-punishing, I think I did pretty well. Since this is mostly a narrative visual novel, I'd put a lower priority for it compared to the writing/narrative.
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End of Spoiler
Overall, this is a decent visual novel, I enjoyed my time playing it and made it until the end of Day 1+ the 10 questions personal assessment. Although the pacing is too slow for my taste and the content is still lacking, it is an overall pleasant experience to go through the demo. I do look forward to know what will happen in the full demo!
Good luck on the development!