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?