Yunshan is rife with spiritual entities. It is a magical place with much higher concentrations of otherworldly beings within its boundaries. These beings are known to the people of Yunshan collectively under the broad label of spirits. This label is very general, and can lead to a lot of confusion and misunderstandings about what a spirit is, and how it should be interacted with. What is a person who plans on bumping back to do? Educate oneself. Following is a brief breakdown of the different types of spirits and some info about the unique characteristics of each. This is by no means exhaustive, but should help you represent things you would know, and learn at least the basics.
Nature Spirits:
What They Look Like
Nature spirits manifest as everything from towering animated embodiment’s of elemental force, to impish or fairy like beings that resemble the fey of western realms. Nature spirits can 
very immensely in appearance and power from one to the next. In Yunshan, if it’s elemental, or fey in appearance, it’s probably a nature spirit.
Why are they here?
Some say the oldest nature spirits predate the gods themselves, and are just as powerful. They seem inextricably tied to the physical world, usually having influence over a distinct area such as a valley or mountain, and bound to it through a specific location or naturally occurring object within the area, sometimes called a focus. Ancient trees, unusual rock formations, mountain peaks, and rivers are all real world objects that might be the foci for a powerful nature spirit. Nature spirits seem to be bound by ancient laws which are very hard for mortals to comprehend or anticipate. Some suggest the spirits of nature continually build and maintain the physical world for the gods, though one can only guess how they are paid for this service. Never the less, they do care greatly for the regions they inhabit, and have a huge say in what goes on near their points of focus.
How they affect the world
Theoretically every distinct object in nature has a spirit. These spirits exist in the ethereal plane closely tied to the physical location of the material object that serves as their focus. Only the very powerful among the multitude of nature spirits choose to have direct contact with the physical world however, and they do this by forming magical and wholly physical bodies with which to move through and affect the realm of mortals.
Nature spirits who are powerful enough to form material bodies take great interest in the actions of mortals within their region of control. They are very capable of being pleased and offended, and can magically aid or hamper those who operate in their area of influence, depending on how much they like them! Every spirit of nature is vastly unique in temperament and tastes, and the people of Yunshan have learned the importance of knowing how to appease all the major spirits that inhabit the areas they frequent. The rule of both nozufoo and clans person alike, for all time has been, don’t ask why, just do what the spirits ask.
Exorcism
The physical bodies of nature spirits can be destroyed, usually only through magic or weapons made of cold iron. Still, they live on, and will quickly, usually by sunrise, reform, with full memory of who so rudely dispatched them. They will not leave their area of influence to seek revenge, but will be waiting if their slayer ever passes through their area again, and it is said the spirits can smell the blood of those who have wronged them better than any blood hound.
If the focus object that binds a spirit to the mortal realm is destroyed, the spirit will be driven mad with rage. Such spirits, “go bad”, stalking their domains and delivering murderous wrath to anyone they happen upon. It is a known fact that in the past evil men have purposely destroyed spirit foci in order to sew chaos in a region, by unleashing angry forces of nature upon the unsuspecting people who live there. These raging nature spirits can be exorcised, but only skilled spirit shaman, or great spirits of nature themselves seem capable of pacifying a spirit whose foci has been destroyed.
As stated above, the physical bodies’ nature spirits form may be destroyed, but they live on and will merely form again later. Spirits of nature are immortal. They come into and leave the mortal realm independent of the actions of men. For this reason, most seasoned demon hunters and pious priests do everything they can to avoid a fight with such a spirit. After all, under divine law, nature spirits are given authority to act as they do in their places of influence. In a confrontation with a nature spirit, a demon hunter will first try to appease or negotiate, and if these do not work will try to circumvent or flee. It is certainly permitted, and even expected that a demon hunter will fight and destroy a spirit which has gone mad.
Gaki Spirits:
What They Look Like
Gaki usually appear as ghoulish, corpse-like humans that vaguely resemble the person they were in life. In low lighting, they might pass for humans, but their features are often slightly bestial with sharp teeth and hard, blackened nails that serve as claws. Their eyes are often strange or wild in appearance as well. Most gaki seem to show signs of rot, and smell like they do.
Why are they here?
One story goes like this: During the age of blood, when Yunshan was ruled over by the Shinto Kings, the land was full of corruption, and evil men were literally getting away with murder. The heavenly courts were flooded with wicked spirits who had gotten away with their crimes and never been punished by an earthly court. Apparently, people who get away with their crimes in life require a great deal of extra paperwork on the part of the heavenly courts to be properly tried for their crimes in heaven. As a result, the legal proceedings in heaven bogged down and things were starting to fall off schedule!
Chu Jung, supreme judge of the heavenly courts, was greatly angered by the failure of mortal priests and earthly authorities to bring criminals to justice on their own plane. Tired of having his clerks tied up writing and filing vast amounts of extra legal scrolls, he angrily declared a new law.
Any mortal who commits a felony sin and who in his life time is not judged and punished by his people for said act, or who does not take some proper act of atonement properly sanctioned by an earthly authority to make amends for said sin, shall, upon death, be immediately cast back to life, in vile form sufficient to represent their sin, and cause them great hardship, and cause great menace to the mortal realm as a punishment for those peoples who failed to provide proper judgment and or atonement for said soul. These Gaki, or rejected souls, shall roam the mortal realm spreading evil, as a punishment for society’s lack of integrity, and shall live on forever, unless hunted down and destroyed, and thus, judged and made to pay for their evil by mortal authorities, as should have been accomplished in the first place!
How they affect the world
Gaki are one of the most feared spirits in all of Yunshan, not because they are the most powerful, but because they hunger for human flesh. Anyone devoured by a gaki will become a horrible ghost who haunts the minds of his relatives until they go insane unless the offending gaki is hunted down and properly slain. Gaki are drawn to the burial places of Yunshan’s people, and love the flesh of the dead as well. Anyone whose corpse is so snacked upon will suffer the same fate as above. There are old tales of bands of gaki breaking into the burial site of a village and eating so many corpses that the entire village went mad or had to flee. Thus, almost entirely because of Gaki, Yunshan’s people protect the bodies of their dead as best as they can, until all the flesh rots from the bone naturally, at which point the spirit of the deceased is said to have passed on completely to the ancestral lands in heaven, where it no longer need fear such corruption.
When a gaki spirit first awakes in the mortal realm it is both hunter and hunted. It is drawn to work evil upon the living, and to eat the dead, but it also fears being detected and hunted down by a priest or demon hunter. Most gaki “live” solitary lives at the edge of human settlements seeking to feed upon the living and dead, always struggling to keep their blood lust under control to avoid the attention of would be demon hunters or priests. What they fear most is destruction at the hands of a hunter, and the final judgment that will follow. This is their last chance at life, however twisted, and they fight viciously to stay alive. Still, most gaki are hunted down very soon after they arrive. Thanks to the efforts of the great temples the turnover rate for gaki is high.
There are disturbing tales of underworld cities in the mortal realm, and other bizarre settlements ruled by powerful evil spirits, who offer gaki a place of refuge in return for service. These are legends and can only be taken as such. What is known is gaki who manage to survive their first few months often seek out wu jen, powerful spirits of evil, or other gaki to band together with. The old, “there’s a gaki roaming the country side over by such and such”, is a recurring rumor in almost any village in Yunshan. Single gaki, usually already being hunted by the local demon hunter are not uncommon. An entire band of gaki working together is another story altogether, especially if they have found an intelligent master to serve. In such cases, often times it is the demon hunter who finds himself hunted, and entire regions can be paralyzed with fear until the evil is finally overcome.
Exorcism
There is no special ritual involved in exorcising a gaki. It need only be destroyed and it is banished back to the celestial realm to be judged. Doing so is not necessarily easy though. Gaki seem to heal as fast as they are wounded, making them nearly immune to normal weapons. Gaki are vulnerable to spells, and to weapons made of alchemical copper.
Yorei
These most resemble ghosts. They are the spirits of those who cling hatefully to this life because some deed has gone undone, or some injustice unpunished. Yorei are mostly incorporeal, and where usually good people in life, upon whom some horrible death befell.
What They Look Like
Yorei are invisible whenever they wish to be. A yorei will show itself to those who are weak in heart, while remaining invisible to those who are strong willed. This selective invisibility is a unique characteristic that Yorei have as opposed to western ghosts. Yorei attack the sanity of those who can see them first, reaching into the minds of men from the ethereal plane and attacking the victims’ psyche, while haunting the material surroundings with various ghostly happenings. They combine a cat and mouse game of haunting in the real world, while slowing driving their victims neurotic and insane from within. Once this goes on long enough, the Yorei will manifest a terrible physical body and kill its victim.
Perhaps the most striking aspect of the Yorei as compared to the western ghost, is their ability to temporarily take a material form, a hideous, shaking, ghoul like apparition that resembles a twisted undead version of who the person was in life (Think the Ring). Yorei do this when they can no longer hold back their rage and must attack the living.
Why are they here?
Yorei are here for the same reasons as any ghosts. They are the spirits of strong willed individuals who are so obsessed with the nature of their death, that they are unable to pass on. There are many different varieties of Yorei, and on top of this, no two seem to be exactly alike. Some known examples:
Ku Hun or “Orphaned Soul” is the spirit of a child who died alone, and whose body was never discovered by its parents. The immense sadness and terror of the child, the unresolved grief of the questioning parents, and the lack of a suitable burial are all factors which contribute to the birth of a Ku Hun. Such spirits resemble those they did in life, and can easily be identified by those who knew them, but have long fangs and claws they use to attack with.
Li Kuei, or “vengeful ghost,” is the spirit of someone murdered or executed unjustly. This spirit extracts revenge by attacking all who cross its path.
E- Kuei, also known and hungry ghosts, appear as unkempt and starving versions of who they were in life. They are the spirits of those whose graves have been neglected and forgotten. They are angry and will attack immediately after they have tried to charm as many opponents as possible.
How they affect the world
Yorei can be extremely powerful and tricky opponents. Thankfully, in almost all known cases, they are tied to a specific area and do not wander beyond it. Thus, when a Yorei is suspected to inhabit a place, the locals simply avoid it until they can raise enough money to hire a demon hunter.
For the same reason Yorei can be avoided, they can also go unnoticed. Would be adventurers should know the wilderness is dotted with forgotten burial grounds, and old ruins, both places where Yorei might lay in wait.
Exorcism
Yorei cannot simply be destroyed. Doing this only solves the problem for a short time. Unless the ghost is properly put to rest it will reappear again and again. To put a yorei to rest is a dangerous task. Most adventurers who don’t run from a Yorei simply settle for destroying the thing with magical and physical force. They move on, thinking their job done, but in a few months, or sometimes even the next day, the restless spirit they thought they destroyed simply reforms and takes up its old haunt. Only those educated on Yorei, and dedicated to putting the dead to rest, attempt a true exorcism. Exorcism not only ends the unruly spirits rampage on this earth, but also puts it to rest, allowing the spirit to move on.
An Exorcism has 3 steps, which can be performed in a few rounds, or might take weeks, depending on the spirit. Here they are. If those attempting the exorcism have the original mortal remains that belong to the spirit, they may skip step 1.
Step 1: The Subdual
Even the weakest yorei is a powerhouse of supernatural rage. In order to put the spirit to rest it must first be sufficiently weakened and subdued. Often this step is as simple as the destruction of the yorei’s body through magic or force of arms. Many Yunshan spirits form physical bodies, and these often must be slain before the spirit can be exorcised. In some cases, the spirits body, whether corporeal or incorporeal, must be destroyed by a particular type of energy or weapons made of a particular substance. Yorei are usually vulnerable to either alchemical silver, copper, or jade weapons. Only very experienced demon hunters know how to tell which. Those who don’t must resort to trial and error. At any rate, once the spirits body is violently destroyed, its will power is sufficiently weakened to allow the exorcist to move on to the next step. In many cases, a successful turn undead attempt will subdue the spirit. If those attempting the exorcism have the original mortal remains that belong to the spirit, they may usually skip this step. This is perhaps the easiest way.
Step 2: The Interrogation
In which the spirit is forced to make contact with those who are attempting to exorcise it. After the Subdual, a spell must be cast on the spot the ghost was destroyed/subdued. Any of the following spells will work; speak with dead, protection from evil, exaction, control undead. In some cases, a specific, rarer spell must be used. Once the proper spell is cast, a very faint version of the spirits body will immediately reform in the place where it was destroyed. The demon hunter has already defeated the spirit physically, now a battle of wills must commence. In this battle the exorcist must convince the spirit that its presence in this world is unnatural, and it must move on to the next. The Yorei must be bribed, cajoled, intimidated, or sweet talked into accepting its fate, and giving the demon hunter information as to what must be done to help it move on.
This battle of wills can be a long stare down, a vicious shouting contest, a duel of riddles, or of wit. It might take a few moments, or hours, every Yorei is different. Whatever form the Interrogation takes, mechanically it breaks down thusly: Priests must make a 2nd turning attempt with a +4 bonus. A non priest must substitute an opposed skill check against the spirit which the DM decides is relevant to that particular interrogation. The spirit of a stubborn warrior might engage the demon hunter in an opposed intimidate check. A tricky spirit who does not wish to be banished might have to be fooled into giving up its weakness, requiring a bluff check. It could literally be any kind of check which pits the exorcist against the stubborn ghost in some way that was relevant to it in life. Often times the demon hunter may choose between several skills the DM lays out as relevant, and use whichever he is best at.
If the check is successful, the yorei must give some indication of what must be done to put it to rest. Some spirits will be very direct and helpful in relying why they are not at rest. Some spirits will be capricious and speak in riddles, while others will be stoic or cranky. Whatever the case, this conversation, however short, is played out and then the spirit disappears. Whether the Exorcist got useful information, or failed his check and got nothing, the spirit eventually slips away into the ethereal plane, only to reform again in 24 hours to wreak havoc anew! If he got good information, he’d better move quickly. If he failed, a demon hunter may try and Subdue/Interrogate the spirit again, but upon failing the 3rd time, usually cannot try again. In this way, it is not unusual for a demon hunter to have to admit failure and be forced to abandon an exorcism, or else find a replacement.
Step 3: The Unwinding of Discord
Now the Exorcist must take whatever information they have been given and try to do what is necessary to put the spirit to rest. If they cannot complete these tasks the spirit will reform in 24 hours, newly enraged, and will often interfere with the very people trying to help it. The exorcists may attempt to subdue and interrogate the spirit again, as many as three times to further question it and gain new clues. Common requirements for The Unwinding of Discord include, finding and properly disposing of the spirits original body, exposing the one who killed it to the authorities, or delivering an item or message of great importance to a living family member.
Celestial Spirits:
What They Look Like
Celestials are said to be the children of the gods. They are extremely powerful and only accomplished demon hunters/ priests seek them out for knowledge or combat. Nor should the word celestial give the impression that they are all good. It merely points to the fact that these creatures have their origins in the spirit world, and are closely tied to the divine and mysterious power of that place and its’ gods. Ki rin, and oriental dragons are all Examples of Celestials.
Why are they here?
Celestials guard holy places where men are not supposed to go. An interesting concept is the idea that if a mortal can defeat a 
celestial in honorable combat, he has won the right to pass into the place that is guarded, or to take some item the Celestial was protecting. There are many stories of mighty priests who climbed some high mountain, or descended the depths of some legendary cave to fight a celestial. In these legends the mighty celestial is humbled by the heroes’ prowess and piety, and honor requires the powerful spirit to give the mortal hero what he seeks. Examples include an audience with a particular god, gaining the right to travel though the spirit world, the answer to a question only the defeated spirit knows, or the temporary use of some mighty relic, these are all prizes frequently spoken of in these legends of heroes.
How they affect the world
Celestials must certainly have a great deal of influence on the mortal realm, yet it is not obvious. They rarely leave the spirit world or show themselves to mortals. When they do, mortals had better pay attention, because something huge is underway!
Exorcism
Celestial spirits are said to be immortal. When they enter the mortal realm they form incredibly strong physical bodies. Celestials can be affected by spells, but are extremely resistant to them. Their only one real weakness is magically enchanted weapons made of jade.
Demonic Spirits:
What They Look Like
Like celestials, this class of spirits is extremely varied and extremely powerful. While most commoners use the word “demon” to refer to any hostile spirit, demon hunters are more particular in how they use the word. Any spirit which is powerful, corrupt, able to manifest a physical body with which to torment the mortal realm, and that does not fall into the above categories, is generally regarded as some type of Demon. Oni are a perfect example.
Why are they here?
No one knows. No one knows why these menaces are here, only that great priests and demon hunters are needed to ferret them out wherever they have surfaced to spread murder or hatch nefarious plots against mankind. There are many legends, many of which you will no doubt hear as time goes on…
How they affect the world
True demons are rare, especially in western Yunshan, and like celestials, their presence should give men pause. They are to be destroyed no 
doubt, yet they must be approached with respect for their power. Note, a demons decision to mettle in a region in a way that gets it noticed often betrays the presence of a larger, more dire evil at work.
Exorcism
Like Celestials, Demons are vulnerable to Jade weapons. They often have some immunity to magic, but are not nearly as protected as celestials. Find a type of energy which hurts them, and blasting is a completely valid tactic, though they will not go down as easy as mortal monsters.