The Hunterverse — also sometimes called Rankerverse — is a type of dungeon crawler trope popularized in South Korean fiction. Hunters are “awakened" individuals who typically possess abilities that they’re able to use to fight and kill monsters and alien creatures.
Most Hunterverse stories start with, or mention the sudden occurrences of gateways (or portals) opening from which monsters and alien creatures appear from alternate dimensions. This phenomenon tended to also coincide with the " awakening” of certain individuals who gained supernatural abilities of some kind.
These people were called "hunters" (or "rankers") and they were mainly tasked with protecting the world from these monsters and alien creatures that escaped into the real world from these alternate dimensions — typically mama rich worlds, which is suspected to be the main reason why and how hunters got their powers.
These first batch of hunters were typically called first generation hunters, because they were the first to awaken, and were there when the first gateways opened. Second generation hunters were typically those that were still kids/teens when the gateways first opened, or they might have been the proteges of the first gens after they were either killed, retired or promoted outside of the front lines.
Some stories focused on first generation hunters, other stories focused on second generation hunters and sometimes mentioned only first gen hunters, and other stories didn't specifically focus on eitner first gen or second gen hunters — and of course there are stories that focused on hunters far into the future (who would probably be considered tenth gen or something similar). It really all depends on the author and their worldbuilding.
There have been a lot of different ways and settings authors have worldbuild for their hunter novels, though the settings I've seen the most so far were:
DUNGEON INSTANCES (or Dungeons for short) - They're the main type of setting I've seen so far and they can open anywhere at any time. Dungeons are much more common compared to the other types of settings and usually hunters can only level up their rankings by entering and defeating dungeons and/or finding any items (or artifacts) that can only be found within the dungeons (in some worldbuilding, it's against the law for hunters to use their abilities outside of dungeons).
Some dungeons also have different rankings that only allow hunters of a specific ranking to be able to enter them, and while a dungeon raid is in progress, entry or exit to that specific dungeon is barred until either the dungeon boss is defeated or all the hunters within the dungeon are killed — though there are dungeon items (or artifacts) that can allow a hunter enter or exit a restricted dungeon if ever necessary.
While dungeons are not as world threatening as rifts (or gate shocks or gate burst), because the monsters within the dungeons typically can't escape into the human world like those from rifts can, they are still dangerous and life threatening, especially to lower ranking hunters.
RIFTS - Rifts (or gate shocks or gate bursts) are a much more immediate threat compared to dungeons and towers because those monsters either don't immediately leak into the world or they only spill out from the dungeons or towers when they're mismanaged, meaning hunters (or the government) haven't been “clearing them out” regularly.
If hunters don't defeat the boss and close the rifts in time, even worse monsters can spill out of these rifts and destroy the world as they know it.
TOWERS - This is a setting I haven't seen explored that much so I don't have a lot of knowledge on them, but from what I’ve seen towers are similar to dungeon instances and the difficulty level of the towers increases with each floor a hunter goes up.
Like dungeons when a tower raid is in progress entry and exit to the tower is restricted until the boss is defeated or all the hunters within the tower are killed. Unlike dungeons that are almost a day-to-day occurrence, Towers don't appear that often — sometimes they can even appear only once every three or five years.
Like I said these are just some of the settings I've seen explored the most within the Hunterverse, it's up to you to decide whether you want to utilise just one of the settings, more than one or come up with your own. The same goes for the type of monsters that come out of these gateways, I've seen mythical/fairytale type monsters (like minotaurs, zombies etc.) I've seen alien creatures and I've seen plot specific monsters, again it all depends on your worldbuilding and what you want to use for your story!
Anyway, as hunters turned out to be the only ones who could kill the monsters and close the gateways, a global multi-billion-dollar industry eventually developed around them as a result. Guilds also started popping up and became the hub where Hunters could register as a Hunter and gain access to the perks and other such stuff that came with that.
Guilds can be managed by the government, the military or some kind of corporation and their goal, along with getting rid of the monsters and alien creatures, are to collect the items that can only be found in the dungeons (or rifts or towers) and either use them to raise the rankings of the hunters registered at their guilds or sell the items at a high price. Usually it's both.
(Side note: While guilds are a popular trope within the Hunterverse, your story doesn't have to include the concept of guilds if you don't want it to. You can have hunters be some kind of civil or government job that people have to become if they want to be registered as a hunter or something like that. It all depends on you!)
The Hunterverse often utilises the manwha style ranking systems, which range from S-F rank, with characters always aiming for S-class rankings, because that's the highest ranking, while F-class rankings are considered the lowest — there are hunter stories where the lowest ranking is only D or E.
Like I mentioned, in most Hunterverse stories, hunters are also able to collect items (or artifacts) and special equipment found only in dungeons and bring them back to the real world. These items (or artifacts) are often sold for a high price, and also have a ranking system with the highest grade items fetching even higher prices.
Some Hunterverse stories might also include game-like systems where hunters can gain ability points or progression systems that can upgrade their abilities, raise their rankings and even allow them to purchase special items (or artifacts) if the game system has a store function. Sometimes the systems can only be accessed in a dungeon and sometimes a hunter can use a system whether they're in a dungeon or the real world.
These systems can also sometimes allow hunters to chat with other hunters or even sell the things they've found in their own store, run via the system. In some Hunterverse stories that include game-like systems, the hunters might also have to complete tasks assigned by the system itself to raise their ranks, get special titles, points and so on.
The Hunterverse is usually only about the action and adventure, with the stories following the hunters as they enter dungeons, towers or rifts, battle monsters and alien creatures, raise their rankings and save the world, and romance isn't really a main theme, but there are some Hunterverse stories that have romantic themes as a focus (or sub-focuses) — Though it's usually Guideverse, which is a combination subtrope of the Hunterverse and the Sentinel AU, that has more romance than monster fighting.
Some examples of Hunterverse stories include, but definitely aren't limited to Solo leveling, Murim Log-in, The blade of Evol
ution-walking alone in the dungeon and so on.