If the 'Black Healer Light Novel' has a strong narrative voice, that could be a major factor. A distinct writing style that draws readers in and makes them feel like they are really in the world of the story. It might use vivid descriptions, unique dialogue, and a pacing that keeps you hooked from start to finish, unlike some other light novels that might have a more formulaic approach.
The use of the color 'black' in the title might imply a unique take on the healer concept. Maybe the black healer has a different type of healing power that is not the typical 'white' or pure - hearted healing we often see. It could be something darker or more complex, which sets it apart from other light novels with more traditional healing themes.