I'm not sure exactly as I haven't read it. But generally, a light novel with 'yuusha' (which means hero) in the title might be about the adventures of a hero in a fictional world, perhaps with elements like battles, magic, and the growth of the main character in his heroic journey.
I'm not sure specifically as I haven't read this light novel. But generally, it might be about a protagonist whose job is related to a hero in some way. Maybe it tells the story of someone who has a job that is as great as being a hero, with all kinds of adventures, challenges, and character development.
I'm not entirely sure as I haven't read it. But generally, a light novel with such a title might be about a powerful hero and something related to a 'oharai hako' which could be a special box or container in the context of the story.
Since I haven't had the chance to read this particular light novel, it's difficult to give a detailed account. But based on the title, it seems that the main character is a very strong hero. 'Fukushuu o koinegau' implies that the hero is seeking revenge. In light novels, there are often various sub - genres. This one could potentially be in the action - adventure or fantasy sub - genre. It might also have elements of character development as the hero pursues their revenge, with different obstacles and allies along the way.
You can try looking for it in specialized light novel stores. Some large bookstores might also carry it if they have a section for Japanese light novels.
Well, if you like 'fukushuu o koinegau saikyou yuusha wa light novel', you might enjoy 'That Time I Got Reincarnated as a Slime'. It has a unique protagonist and an engaging story. Also, 'Re:Zero − Starting Life in Another World' is quite popular and has elements like a complex main character's journey, similar to what might be expected in the given light novel. 'Grimgar of Fantasy and Ash' is another light novel that has a group of characters in a fantasy setting, which could be somewhat related in terms of genre.
I'm not sure specifically as I haven't read it. But generally, in the context of 'isekai' (another world) type novels, it might be about a hero who returns from another world and becomes the strongest in the modern world.