Since the Japanese are downstream of submarnites such as myself, one of the older memes on the Japanese internet that has recently resurfaced is the remixing of songs/videos into "Nomurisshu" - a term corresponds miraculously closely to "speaking like Sephiroth," in referring to the Final Fantasy games, Tetsuya Nomura being Sephiroth's character designer.
I've seen Nomurisshu used pretty broadly for chuuni and, at the extremes, even generally archaic prose in general, and perhaps beyond some specific FF lines that gets referenced there is little justification for a firm distinction between Final Fantasy prose and the general chuuni writing style it is readily conflated with. As concerns the FF series proper, however, my impression is that Sephiroth is a massive fucking pseud in a way that is perhaps fortunately not represented in English translation. Or more specifically, that he employs the typical grab-bag of semi-archaizing conventions around chuunibyou/anime speech that has little relation to how actual archaic Japanese worked. (When I see a dubious construction like 選ばれし者 my first thought isn't of any properly archaic register of speech but of anime, for hopefully obvious reasons.) EoParody Sephiroth comes off as stiff in comparison, and perhaps a part of this is the typical crutch of writers to make grand and lofty speech sound formal and circumlocuitous as a crutch, as if one could not have one without turning up the dial on the other. But I don't think this can be blamed on the inability of the English writers to write in a realistically elevated or archaic register per se, for the simple reason that the same could be imputed of the Japanese. It is more circularly that the more general base of chuuni language does not exist in English, so Sephiroth's mixture of different registers feels disjointed and lacking in rhyme or reason rather than corresponding consistently to a fairly regular set of conventions for a specific stock character. A Japanese audience knows to a great degree of accuracy what pronouns and particles a haughty fantasy princess would use and it does not bother them that historically that set of pronouns maps more closely onto the language of 19th-century Japanese schoolgirls than it does to any historical royalty. The same is true of fox goddesses, medieval knights, and the perhaps more nebulous mould of character from with Sephiroth has been cast. Until a general self-referential base of stock-characters is built up in the Western mind, to "speak like Sephiroth" can be no more than a term of convenience.