Hunters have existed as long as recorded history, likely even longer. Every living hunter is descended from a long line of hunters before them. Nobody is sure who the first hunter was, and nothing suggests that the hunters are related. Even the most meticulously recorded hunter genealogies only go back so far, and no existing records reveal the origin of a hunter lineage. Likewise, there is no recorded instance of a new hunter lineage coming about. Not every child born to hunters possesses their powers. There seems to be a limit to the number of hunters that can exist at any one time. If a hunter is born to two hunters of two different lineages, they will express the abilities of only one or the other lineage, and be considered a part of that lineage.

Hunters possess physical abilities beyond that of normal humans. They are faster, stronger, and more durable but so are the creatures they hunt. It doesn't so much give them an edge as a fighting chance. They also possess magical abilities specific to their bloodline. These abilities are broad and can range from elemental manipulation, object materialization, physical metamorphosis, or even stranger powers. While each lineage possesses the same overall ability, hunters will often develop their own unique style and techniques by training their ability. So, even though two hunters may be from the same lineage, they may have very different fighting styles.

Hunters also possess weapons called "heirlooms." These take the form of a traditional weapon, be it a sword, a bow and arrow, tonfas, a scythe, etc. Heirlooms are created specifically for their hunter as a rite of initiation. Only one hunter lineage possesses the ability to create heirlooms, so getting a replacement is difficult. Fortunately, heirlooms are more durable than standard materials, and while they can break, it takes an extremely powerful attack to do so. Heirlooms possess magical properties that make them particularly effective against youkai, and have a minor ability that often compliments a hunter's magical abilities. An ice user's heirloom, for example, might be cold enough to induce frostbite when it strikes. An heirloom's abilities can only be activated by someone with the blood of the correct lineage, so trading heirlooms isn't feasible.

Hunters are considered ready to take up arms when they turn 14. Upon coming of age, hunters swear an oath to follow a simple, yet strict set of rules: 1.) A hunter will never use their powers to harm a human. 2.) A hunter will never reveal the existence of youkai to humans. 3.) When called upon, a hunter will take up arms to destroy youkai.

If a hunter breaks their oath, they will be put on trial for their actions and judged by the community. In some cases, it is deemed that there were extenuating circumstances and the hunter acted reasonable, and a pardon will be issued. If this is not the case, though, the hunter will be branded a traitor. They will be given an irremovable mark on their forehead and will be excommunicated from the community. If they are found causing trouble, they will be treated as a youkai. Similarly, if a hunter refuses to take the oath, they will be excommunicated and barred from using their powers, though they do not need to bear the mark of dishonor.

Hunters are organized into four ranks. Hunters of lower rank are expected to respect and follow the instructions of hunters of a higher rank.

Kagayakuha: These are the hunters who have recently taken their oath. They have received training in how to fight and use their powers, but they still have much to learn. They operate in groups like The Hunter's Club, and are urged to fight as a team while they grow. The group is typically assigned a mentor to give them advice and help them grow through further training, but they are left to fight battles on their own.

Nenshouha: These are hunters with years of experience battling youkai and have been recognized as full-fledged hunters. All Kagayakuha attain this rank when they turn 18, providing they spent their years diligently training and carrying out their duties. They are permitted to hunt alone, and it is up to their discretion whether they recruit allies for a hunt. Likewise, they are left to their own devices to further their own abilities. Many hunters never attain the next rank.

Tenha: These are hunters who have attained true mastery of their skills. In order to attain the rank of Tenha, a Nenshouha must pass a rigorous trial. If they fail, they must wait 5 years before attempting it again. Those who achieve the rank of Tenha make decisions that effect the organization as a whole. It is considered very poor form to question a Tenha's decisions, as they likely know many things that you do not.

Kusuburiha: These are retired hunters. Those who have lived a long life of battle and lived to the end of it all are granted this honorable rank. They are no longer fit to fight, but have decades of wisdom and experience behind them. Their primary role is to train and advise Kagayakuha, but even Tenha will often come to them for experienced guidance.

Duels are permitted among hunters, though they are supervised and strict rules are implemented to prevent serious injury. It is not uncommon for hunters to want to test their strength or put their pride on the line against a rival, but the organization will not tolerate any activities that would jeopardize their ability to function. A sporting way to vent frustrations was deemed to be the best solution.

In order to help blend in with humans, hunters are given limiters. These are generally piercings or pieces of jewelry, things that will stay in place, but can be easily removed when the need arises. Limiters nullify a hunter's supernatural abilities, rendering them more or less normal humans. Albeit, they still know how to fight, but their strength won't terrify the normies. Likewise, charms are provided for their heirlooms that have similar effects. They can be disguised to look like a mundane object so that they can be carried in public without alarm. A charm can take the form of a key ring, a padlock, or any other tiny object that can be removed easily. So, hunters can at least attempt to have a normal life.

Youkai have existed as long as humans. They are diverse and can take any number of forms, but they are all innately magical. Like hunters, youkai possess physical abilities beyond that of ordinary humans. Each kind of youkai possesses its own set of magical abilities and powers. The range of these abilities is incredibly broad, and the full scope of youkai abilities still as not been documented by hunters, even after centuries of combat. The physical forms of youkai vary widely as well. If there is a piece of human lore about a monster, chances are it is derived from a true story about an encounter with a youkai. One ability they all share, though, is the ability to take on a humanoid form. Youkai can look almost human with their magic, and with the right disguise can walk among crowds unnoticed. However, they all have their own "tells," revealing what they really are.

Contrary to popular believe, most youkai do not have exceedingly long life spans. Depending on their species, they live about as long as humans, do. However, some exceptionally powerful youkai have unlocked the secrets to longevity and have lived for centuries. Youkai can interbreed with other species of youkai and their offspring will take on the species of either the mother or the father. Youkai can breed with humans as well, and the offspring becomes a youkai. If a youkai breeds with a hunter, the offspring will be either a hunter or a youkai.

The dispositions and personalities of youkai are as diverse as humans'. Some youkai are kind and benevolent. Others are cruel and bloodthirsty. Those that cause trouble for humans are targeted by the hunters and eliminated. The hunters have means of detecting when youkai enter the human world. When they do, hunters will be sent to assess the disposition of the youkai. A youkai is permitted to live peacefully among humans if the follow simple rules similar to the hunter oath. They may not use their powers to harm a human, and they may not reveal the existence of youkai to the humans. They have the choice of living in isolated areas where they are unlikely to encounter humans, or they may integrate into human society. Those that choose the latter are given a charm that fully disguises them as humans and functions like a hunter's limiter. It also doubles as a tracking device, monitoring their location, so the hunters can keep tabs on youkai in the human world. If a youkai breaks these rules, they will be hunted and destroyed.

Many youkai come to the human world for less peaceful reasons, though. Cases of humans being "spirited away" still occur and only the hunters know the truth of these instances. Some youkai are able to elude detection when they enter the human world, or are strong enough to fend off the hunters that come after them. A youkai like this only lasts long by being crafty as well as powerful. They are very good at concealing themselves. Fortunately, hunters can detect a youkai's aura, so they'll know if one is nearby. Hunters can use this ability to engage youkai before they start harming humans, keeping the "spirited away" cases to a minimum.

In their native realms, youkai form little societies. The youkai that enter the human world represent only a very small percentage of those that exist, and even then are those that did not fit in well with their societies. Some youkai have shared knowledge of their native realms with the hunters, but their knowledge on the matter is limited. Hunters are not popular in youkai realms and any prolonged excursions there, even for peaceful research, are incredibly dangerous.