Why would 《 and 》 be used in a translation?

Question

In Shikkoku no Sharnoth ~What a Beautiful Tomorrow~, some words like Metacreature, Illuminati and Old One have 《 and 》 on either side. you can see them on Part 3-1 of the Web Novel

I feel like this black form is the same as those 《Metacreatures》.

and here on the index page

the 《Omnipotent》 man (his name is Leo)

now at first I thought this was a style choice by Amaterasu Translations since Hikari no Valusia ~What a Beautiful Hopes~ hadn't been translated (and Amaterasu Translations said they may do them one day) however it shows up in Aoishiro when words like 《Sword》, 《See》 and 《Power》 and it was translated by Shijima. The 2 Visual Novels are also done by different groups.

Now I would get it if it was just name, however 《Power》 doesn't seem to be a name as it's normally used to describe what a lot of the heroines are taking from drinking Shouko's blood or what Yasuhime-sama receives from the trees she planted.

So is the use of 《 and 》 a style thing for translators outside of Japan or is there something in the Japanese language which calls for the use of these?

Answer 1

It's the same way in the original. The line about "Metacreatures" is:

黒い塊は、それら《怪異》と同じように思えた。

So in this case, it's probably just a matter of the translators using the original punctuation (you will notice that they do the same thing with dialogue, using 「」 as in the original rather than “”, which is standard in English).

As for why the original itself uses 《》: Logan is right that these are not typically used in Japanese:

These are Guillemet marks, which are used as quotation marks in some languages like French and Greek (notably not typically in Japanese though, which uses 「．．．」, though they can be used sometimes and are referred to as either 二重山がた [ni-juu-yama-gata "double mountain-shaped [brackets]"] or 二重ギュメ [ni-juu-gyume "double guillemet"]).

《》 are basically used however the author wishes to use them (e.g. this answer on Japanese.SE shows one way that 《》 is used in a Japanese dictionary). I'm not familiar with Shikkoku no Sharnoth, but a quick skim of the web novel suggests that the author is using 《》 to surround proper nouns with a specific in-universe meaning, like 怪異 ("Metacreature"?) and 大消失 ("Vanishing"). Kind of like how we would (and the translators do) use capital letters to identify proper nouns in English. Japanese doesn't have capital letters, so the 《》 is an alternate way of achieving the same effect.