Every specialized field has its own jargon. When translating from a foreign language, it is important to know the vocabulary that is particular to the document under analysis, whether it is scientific, historical, or literary in nature. The genre of fantasy literature is especially complex because it draws upon a wide range of mythologies and religions as well as authors' imaginations. Such words are not likely to be taught in language-learning classrooms or texts because they are not often heard in daily communication. I have compiled here a collection of Japanese words that appear frequently in fantasy literature, along with explanations of their meaning and background where appropriate.

First, it is necessary to explain the way the Japanese written language works. The set of characters borrowed from Chinese, called kanji, stand for individual words or concepts. They frequently have from two to four possible pronunciations. This is because they may have had more than one pronunciation imported from China, then gained an additional pronunciation from the native Japanese language. Individual sounds may also change due to the linguistic environment, generally because of the sound that directly precedes the word. The correct pronunciation is commonly indicated through the use of the hiragana syllabary, in which each symbol represents one syllable. There is also a second syllabary of katakana characters, most often used to spell out foreign words, but also used for emphasis.

In the first section, I will list kanji that not only have their own individual meanings, they can also be combined into compounds to form new words. In later sections, I will give examples of the most common of such compounds as well as words that fit other classifications.

bad, evil
thing, object
(o)majinai, noroi
curse, magic spell Though it ranges in meaning from curses or hexes intended to harm others (noroi) or good luck charms meant to protect people (o-majinai), the character ju refers to spells that are cast in one way or another.
jutsu skill, technique
animal, beast The kind of beast implied by kemono is usually a large mammal of some kind, generally fierce, although other types of creatures such as reptiles or birds may be included if they are big and fearsome enough.
ka, ke
to change The verb forms of this word, ka suru and bakeru, can mean simply "to change" or "to transform." However, there are overtones of the supernatural involved. The noun o-bake means "ghost." Often, if a person threatens that he or she will bakete deru ("to change and appear"), the meaning is that the person will turn into a ghost and haunt someone.
supernatural, superhuman, suspicious
kai world Rather than "planet," this is used to represent a more abstract meaning, more along the lines of "realm." It is very similar to "dimension" as used in the phrase "alternate dimension." In fantasy, it is a suffix to describe the worlds or dimensions of various races, such as "human world," "demon world," and so on.
ki, ke mind, energy, aura The definition of ki is difficult to translate into English because it has so many different usages. It can refer to one's thoughts, intentions, or inclinations, yet it can also describe one's intrinsic energy or life force. The word "aura" comes closest to capturing the way it is used with respect to magic.
demon, ogre An oni is a specific kind of demon that is usually bipedal and often has one or two horns. However, the word is also used to describe a mean or cruel person. It is a common theme that a human who has strong enough hatred will turn into an oni. Interestingly, small oni are often cute and relatively harmless, though they may be pranksters, very much like fauns or gremlins.
ma magic, evil The meaing of this word ranges from neutral "magic" to very negative "evil," and it is sometimes difficult to determine the author's intent. When used alone, it is frequently negative, referring to magic derived from dark or demonic sources.
nin, jin
person, human
rei, ryou spirit, ghost This term typically refers to the spirit--either living or dead--of a human or similar animate being, in contrast to sei (below).
ryoku, riki
power, strength, energy
sei spirit Japan has a tradition of animism, the belief that everything has a spirit. Sei describes the spirit of an inanimate object, a plant (particularly trees), or an element such as water or air.
shin, jin
god "God" in this sense is any being originating in the human world, afterlife, or "heaven" (see ten below) with vastly more power than humans. Gods are often associated with specific geographic regions and are sometimes confined to an area as small as a single temple or holy relic. They can be both good and evil, but they are distinguished from demons in that their power is "holy" (shin) and not derived from ma (above). Rather than being omnipotent, most gods have particular talents and weaknesses. Izanami and Izanagi are a pair of deities said to have created Japan. Inari is a deity of the harvest.
ten sky, heaven The word ten can refer to the sky in general or the "realm of the gods." This version of "heaven" is exclusively a place where gods live and is completely separate from the human afterlife, much like Mount Olympus.
ayakashi, ayashii
supernatural, bewitching, monster This describes a type of monster or demon that is associated with magical power but is not necessarily evil. An analogy from Western mythology would be the creatures of Faerie, who often consider humans to be lower life forms and can therefore appear cruel from a human perspective. They may or may not be able to take on a human appearance, but if they can, it is often supernaturally beautiful.