Kyoukai no Kanata contains a few terms of art for which I have invented English analogues. Now that I've released part 2 of chapter 1, which contains a number of these terms, I think it's appropriate for me to identify them and explain my rationale for selecting them. I have done so here - check after the jump.
異界士 (ikaishi: xenor) - this term describes people like Mitsuki, Akihito's mother, and others who fight dreamghasts. Decomposed character-by-character, 異界士 means other-world-warrior. Decomposed morpheme-by-morpheme, xenor breaks down into foreign/other (xeno-) doer (-or, an agentizing suffix).
I have excluded the "world" meaning from my analogue of ikaishi because 1.) I could not find a sufficiently cromulent rendering that included tha meaning; and 2.) the word xenocosm captures the notion of "world" effectively anyway. ikaishi has no precedented usages in Japanese, aside from other people independently inventing the word for their own fantasy settings.
異界 (ikai: xenocosm) - this term refers to the realm to which dreamghasts and ghastlings are sent. Character-by-character, 異界 means other-world. Morpheme-by-morpheme, xenocosm is foreign/other (xeno-) world (-cosm).
This term does see some use in ordinary Japanese - ikai is used in academic discussions of mythology as a blanket term for otherworlds mythologically posited to exist, such as Hades in Greek mythology, or Yomi in Shinto mythology. Typically, it refers to a "spirit world" or "world of the dead" or something along those lines. I think it's also used in psychology/sociology to refer to "the Other", but I don't really want to dig through postmodernist psychobabble (in Japanese, at that) to figure out what the details are on that front.
妖夢 (youmu: dreamghast) - this term describes entities like Akihito's father and the 虚ろな影 (to be explained in a later blog post). They are, of course, the creatures against which xenors fight. Character-by-character, 妖夢 is supernatural/strange-dream. 妖 appears in words like 妖怪 youkai (roughly, ghost/spirit/apparition). The morpheme-wise decomposition should be obvious.
The word "ghast" doesn't really have any particularly strong connotations (outside of D&D circles) besides being creepy and sort of ghostly, which is pretty much how youmu are said to be. In this sense, it is a better choice than "ghost", since people have more pre-existing ideas about what a "ghost" is. I'm not entirely convinced that "ghast" is the best choice here, but it's the best I could come up with.
Aside: this has nothing to do with the 2hu character "Youmu Konpaku", who shares the same name.
妖夢憑き (youmutsuki: ghastling) - this term describes people who have been possessed by youmu. This one breaks down as youmu-possessed (cf. by analogy 悪魔憑き akumatsuki "one who has been possessed by a demon"). Here, -ling is a diminutive suffix (youmutsuki are in a sense lesser to youmu), with the added connotation of "one who follows" (e.g. ducklings follow a duck; underlings follow their leader; etc.), which is as close as I could get to the idea of "possessed" without using something like "dreamghast-possessees" or something absurd like that.
Broadly, you will note that I have tried to use Greek- and Latin-based roots for things relating to ikai, and Germanic-based roots and words for things relating to youmu. The novel doesn't really have an analogous distinction in the original Japanese - the analogous distinction in Japanese would be between kango and wago, or Sino-Japanese and native-Japanese words, but all the words I've discussed above are kango. Nonetheless, I thought this would be a nice stylistic flourish.
I'll be making another post like this once I've progressed far enough in the translation as to have a few more terms of art that are in need of explanation. That should happen around the end of Chapter 1