[SPIRITS]
Spirits are the physical manifestations of peoples wants or desires. Think of them like addictions or vices. Usually in the form of a glowing orb of light, they "haunt" people to make them addicted to one particular thing, usually the name of the spirit. Only spirit mediums can see spirits.
For example, if you suddenly feel a great desire to eat a lot of bread, you might be haunted by a bread spirit.
[RULE ONE] For the person to be freed from the haunting, they must get an exorcism performed by a spirit medium. How hard a spirit is to exorcise is based on how many people want what the spirit is named after. A weak spirit can be resisted through sheer will power, a may not even be noticeable.
For example, if you write bread on your shopping list, you are directly feeding the bread spirit and making it harder to exorcise.
[RULE TWO] For spirits that are a specific version of something, desires would contribute power to the specific spirit, and the general spirit(s) that the spirit can be categorized into.
For example, if you want white bread specifically, then you'd contribute power to the white bread spirit, the bread spirit, and the food spirit.
[RULE THREE] Spirits cannot be named after living creatures, or social concepts like 'brother' or 'husband,' but can be named after dead creatures. Spirits can affect how much you like a person.
For example, if you're haunted by the beard spirit, then you might find someone with a beard much more attractive.
[RULE FOUR] Spirits cannot be killed, an exorcism merely removes them from a host. (a rare exception to this rule, if nobody even holds a smidgen of desire towards the thing the spirit is named after, then the spirit will cease to exist, but as soon as someone wants it again, the spirit will be reborn.)
[RULE FIVE] Although there is only one true spirit of any specific concept, they can haunt multiple people at once.
[RULE SIX] The more powerful a spirit is, the more intelligent, some powerful spirits can even speak. The most powerful spirits, known as gods, are given human shaped vessels. These powerful spirits are generally at the very top of the spirit 'food chain,' I.E. Love, Power, and Wealth. These spirits do not need to haunt a person to influence them.
Because of the nature of these spirits, they remain myths in the world of Cupid Part-Timer,
[RULE SEVEN] Spirit hauntings are generally random, but hauntings cannot force people to desire what they do not know or have access to.
[SPIRIT MEDIUMS + EXORCISMS + HAUNTINGS]
'Spirit medium' is a job in this world, which can only be performed by somebody who can see spirits. About one in every ten people are born with the ability to see spirits. It is a spirit medium's job to exorcise spirits, or dispel them from a person. This process can be extremely simple, or it can be extremely hard, depending on how strong the spirit is.
An Exorcism is a ceremony that expels a spirit that is haunting a person. The steps vary with cultures and influence, but generally it starts with the client being put into a deep sleep, (traditionally with hypnosis, but drugs are used for stronger spirits) then the medium's soul leaves their body and enters the body of the client, where they will look for and exorcise the spirit. When they find the spirit (in the form of a small glowing orb somewhere in their body) they must guide the spirit to the outside world. Weak spirits cannot venture further than a few centimeters into a body, so they are considered easy to exorcise. Additional objects are often used to help the medium guide their spirit, but it's unsure if they help.
The process can be very dangerous, the medium's soul is a physical object about the size of a pea, and can seriously damage internal structures if it touches them. For powerful spirits that hide deep inside the body, special surgery is done to provide an easy and safe entry point into the client, but, the spirit needs to be pushed out of a natural hole in the body, IE the mouth or the anus.
Super powerful spirits known as gods cannot be exorcised because they haunt people remotely. Because of how dangerous exorcisms are, spirit mediums are required to spend four years in university and receive a spirit medium licence before they can even oversee an exorcism.
[GODS]
If enough power is given to a spirit, then they are given a human-like vessel and the power to haunt people remotely. These spirits are known as gods, and are named after general concepts such as Love and Food. As you already know, the more powerful a spirit is, the smarter it is, but they're not as smart as you might think. The god of power is about as smart as Albert Einstein.
The vessels they inhabit can be damaged, and they can choose who sees them. If a god is permanently wounded, then they permanently lose some power, meaning the amount of people that would desire that thing would go down.
For example, in the story PTC, the god of love had his eyes removed, which lowered the amount of people that wanted love or anything to do with love. Little is known about these spirits, and in the world of PTC, they mostly exist as folklore.