I don't think most writers when penning monster novels attempt to pick the best type of monster to play on the characters' fears, but they can certainly choose to I guess. I think the best villain would be one that can keep the story moving because it's usually the villain that makes the plot. I guess you can kinda say that the vampires reflect Ozaki's fears as a doctor because they bring in a seemingly incurable disease, but that's kind of an ass pull.
Maybe it would be more accurate to say that monsters that appear in dreams reflect specific fears in your subconscious. Usually when dreams appear, they provide some sort of insight into what scares the character.

I feel like I should try some VNs now. I've definitely heard of them before, but to be able to make choices in the story sounds like a cool idea. Do they involve the reader then, so the reader is a main character? Or is it like a video game where you pick a character to control?