Without having access to the 'narcissus visual novel', it's impossible to determine the main characters. But generally, in a visual novel, we can expect characters that drive the story forward. Given the title, there may be a character with narcissistic tendencies at the center of the story. There could also be characters who act as foils to this narcissistic character, perhaps more empathetic or selfless characters that contrast with the main character's self - absorption. There might also be characters that are part of the narcissistic character's social circle, like colleagues or acquaintances in the story world.
Since I haven't experienced the 'narcissus visual novel', I can't tell you exactly who the main characters are. However, if it follows the theme related to narcissism, we can assume there might be a character who is highly self - focused and perhaps some other characters who are affected by this self - centered character, like friends, family or love interests.