I'm not sure specifically as I haven't read this light novel. It could potentially be about a character (hiraheishi) who dreams of the past (kako). But without more information, it's hard to say for sure.
It's difficult to determine the exact target audience without reading it. But if it has a complex plot about the past like the title implies, it might be aimed at an older teen or young adult audience who enjoy thought - provoking stories.
As I haven't had the chance to read this web novel, it's difficult to name the main characters accurately. But from the title, it seems that the central figure is the hiraheishi. There might be other characters that are part of the hiraheishi's past that start to appear in their dreams. It could also be that there are contemporaries of the hiraheishi who get involved in the story because of the strange dreams. For example, a friend or a family member who notices the hiraheishi's changed behavior due to the dreams and then gets drawn into the mystery of the past that the dreams are revealing.
Since we don't have much information about 'genjitsushugisha no light novel', it could be about many things. It may tell the story of a person who adheres to realism in a world filled with magic or other non - real elements as is common in light novels. This character might be on a journey to either prove the importance of realism or learn to accept the non - real aspects. The story could also involve the character's interactions with other characters who have different outlooks, like the idealists, and how they influence each other.
I'm not very familiar with this light novel specifically. But generally, a light novel often features unique characters and an interesting story set in a particular world. It might have elements like adventure, magic or complex relationships among the characters.
Another option is to check with fan communities or forums related to light novels. Members there might be able to tell you where they got their copy of 'genjitsushugisha no light novel', whether it was from a particular store in their area or an international seller. They may also know of any exclusive or hard - to - find sources for this light novel.