I'm not entirely sure as it could vary a lot. It might be based on the 'Necronomicon' which is often associated with Lovecraftian horror. Maybe it involves a story with dark and mysterious elements, strange creatures, and a sense of the unknown.
Well, the 'necronomicon visual novel' could potentially tell a story that draws from the spooky and often otherworldly concepts related to the Necronomicon. It might have a protagonist who stumbles upon this strange book and then gets drawn into a series of terrifying or mind - boggling events. There could be elements of horror, mystery, and perhaps a touch of the supernatural in it.