Kaminoha Primer

神の刃 "Kami no ha"

Godblade. That is the essence of what it means to be a kaminoha. To exist as a thin razor that splits the spirit and mortal realms from one another. Each and every godblade is a unique bonding of spirit and human, existing due to the instabilities in both spirits that allow them to meld perfectly with one another given the ideal circumstances. These circumstances, once arcane mysteries, have been discovered and exploited by what are known as Edicts to draw out a spirit through the cracks formed naturally in a human soul.
Numbering nine in total, the Edicts are loosely interconnected through a concord at Okumiya Temple located atop Mt. Fuji. Otherwise, they are largely disconnected from one another both in terms of practices and studies. All are united in their most fundamental purpose, however, to keep humanity safeguarded against the predations of corrupt spirits. Their individual traditions and views on the spiritual world are divergent and sometimes conflicting however, even in this regard.
Most kaminoha are viewed as militant aspects of their Edict, priests who bear weapons to protect their faith. This is mostly true, though there are many kaminoha whose knowledge of the deeper details of their faith are somewhat lacking due to their focus on the grueling training required to reach a level of spiritual harmony with their bound spirit.

The Bond

The tie that separates a godblade from most of humanity. Each and every kaminoha goes through three trials - some of which may be completed even before arriving at their temple. Most often these trials are simply presented as natural tribulations of being a part of the priesthood, but reveal their true nature through the final reward. The primary goal, however, of these trials is to introduce spiritual cracks into the user's soul through exposing them to hardship on a physical, mental, or emotional level. These cracks then can be filled from inside by one of the Yaoyorozu no Kami.
Bonding with a kami allows the godblade to bypass the natural immunity spirits typically enjoy when manifesting in the mortal realm. Any weapon wielded by a kaminoha can untether a spirit from its vessel, banishing it back to the spirit realm. More seasoned practitioners, however, may even be able to permanently unwind a spirit's essence - effectively killing them permanently. This bond, also, renders the kaminoha entirely immune to possession.
Further than that, each Edict's bond develops and manifests in different ways. Some bonds affect the physical world through a terrestrial kami, others may even be able to use limited forms of shaped magicks - miracles typically only known by spirits themselves.
Some scholastic detractors of the kaminoha (few that there might be) worry that the bond itself may draw on one's very spirit, leading to a drastically shortened lifespan. While it's true that most kaminoha are fairly young - of thirty years or less - that has far more to do with the inherently dangerous lifestyle that one walks as a warrior. The eldest kaminoha widely known is simply referred to as Ojisan, the elder of the Edict of the Moon.

妖怪 "Yokai"

Also known as akayashi or mononoke, Yokai are the most common classification of spirit. They are defined by their inability to interact in the world in a physical sense outside of very specific purviews. Even an oni can only occasionally force a tree to fall on a farmer, while raiju gather in the skies to cause tremendous thunderstorms. All the while, they remain both invisible and intangible without an object to use as a vessel. Any spirit can find a vessel if it fits their arcane specificities, allowing a gate through which a spirit - malevolent, mischevious, or benevolent - to slip through into the mortal world.

悪魔 "Akuma"

Rarer than most types of spirits, akuma are bedeviling spirits most able to possess mortals. Through trickery, intimidation, coercion, or other methods they find a vessel not in an object, but in a human being. The person's psyche is then fully subdued either partially or completely. The most commonly found cases are that the vessel is in control of their body during the daylight while the Akuma takes control during the night time hours but many are unique to their type of akuma. Unlike yokai, akuma are almost entirely malovelent spirits due to some implicit nature of their makeup.

神 "Kami"

The common definition of kami is quite broad, describing the elements of the world that mortals use to survive. They are natural spirits, both good and bad, that make up the natural elements of the world. What the kami truly are is difficult to discuss, as even among kaminoha only the Yaoyorozu no Kami are truly known - and even they do not truly know what they are due to the method by which they are brought into the mortal realm. As best as can be established, the kami make up the natural order of the world and are so integral to its function that they require truly arcane circumstances to manifest.