たとえば一：
D. Gray-Man まんが
Tyki (antagonist character): コイツ(said to the protagonist)
こいつis a 日本語 word that is written in カタカナ, and it identifies a person with contempt, a word with negative connotation. This word was most likely written in カタカナ to denote emphasis on the word itself, and how the antagonist feels about the protagonist interfering with his plans. This word could have also been written in カタカナ to emphasize masculinity and the 'evil' that the antagonist represents, with the sharp, cutting lines that denote the word.
たとえば二：
はつねみうのPoster (released in 日本）
The katakana to analyze:
アイテムフレカラーイストand ブツク
I could not find what this means in English on the Internet, but seeing as it talks about a CD/DVD/book set, I think it means full-color illustration. Also interesting to note is that the poster spells book in カタカナ as well instead of the simple kanji. This poster was originally distributed in Japan, so it had no reason to have these words in カタカナbut I think that the poster writers wrote it this way, again, to emphasize the word in カタカナ. Books are included in CD/DVD sets when they are limited edition or for special copies, so for it to be included here denotes the product as unique and the カタカナ could attract more potential buyers. The same could be said for the full-color illustration, which is uncommon as well.
The poster is for Hatsune Miku, a popular pop singing hologram (a product of advanced voice software) whose fans are young adults. Hatsune Miku is propagandized as an object of the future, and Western ideas and concepts are associated with that theme, so that Western civilization appears linked to modernity and the future. That could be the reason why these words are written in カタカナ, in order to create a connection to Western culture and further support the idea that Hatsune Miku is modern and futuristic.
I think each textbook is different in explaining the concept of カタカナ because of all the varied and uses that カタカナ has in 日本 culture, such as for emphasis, onomatopoeia, loanwords, foreign words, etc. In the first textbook example, カタカナ is described as consisting of loanwords and onomatopoeia, but the text does not describe it is such specific terms, only giving two examples. The second textbook excerpt also just describes カタカナ for foreign names and loan words. The third example actually mentions a vague descriptions, that カタカナ is used for loanwords, onomatopoeia, and for emphasis by the writer. The last textbook gives the most detailed example, dedicating a whole section to カタカナ. This is most likely because that particular textbook teaches カタカナ separately from the other forms of writing. Overall, the textbooks are also an introduction to 日本語 and a vague (or too categorical) description of カタカナ could confuse the student learning 日本語 and may make them disillusioned about ever learning the language well.
Anyway, that's my analysis, what do you guys think?
じゃあまた！
