This really captures the feel of classic visual novel games. You absolutely nailed the atmosphere.
One thing I think could make it even more immersive is giving the player the illusion of choice. For example, at the beginning, the phone rings and the player has no real option but to answer it.
In games, we often guide players toward the outcome we want anyway, but the important part is making them feel like it was their decision. Right now, the game makes it obvious that you're forcing the interaction, which slightly breaks the immersion. Even if ignoring the phone eventually led back to the same outcome, simply allowing the player to make that choice would make the experience feel much more natural.
Other than that, great job!