It feels like WK, hiragana words being written with kanji.
It’s more “cool”?
It’s not all that surprising that in a setting with a 魔王軍 that words like 此処 would appear. I see stuff like 貴方 and 其方 in kanji all the time. I once even saw 御前 in full kanji so that it was properly distinguished from お前, which was also used in that book. (As in, 御前 implied old usage / respectful language and お前 implied new usage / rough language.)
Besides, at least in the case you encountered it comes with the furigana, so it’s a good opportunity to learn the kanji versions!
Might also be a characterisation thing. Rin in Yuru Camp tends to use kanji for usually-kana words too.
Sounds like her.
Most likely for flavor and style.
And possibly because looking a string of kana is painful when you could use the kanji? But then two lines over, all kana.
That doesn’t explain the fact that it’s almost always written with kana. If anything it makes the flow somewhat worse off.
As others have said, it is probably just a stylistic choice. I just hate kana strings.
Maybe it just provides extra emphasis or makes that specific place stand out more (as a particular ‘here’). Alternatively, it could be characterisation, as someone else has said, and might also be meant to make the character seem… more intelligent/knowledgeable? I’m not sure. It also depends on how consistently this character uses 此処 instead of just ここ.