I am planing to make a Visual Novel Game using RenPy and was wondering, how do I make the story immersive to the players playing?

In this Horror Game, there will be drama, thrill and mystery to solve. You are playing as one character and interacting with a couple NPCs.

So what I am really asking is how do I make the charcter’s in the game likable and hate able to give off that feeling of “you are inside the story and not just watching a movie”. Is it the story, is it the dialogue or is it the graphics? or just something else that I am missing.