Firstly, you cited a passage from a FANFIC (!!!), which is not manga and has only a tenuous connection to it. It's a fantasy story based on the work, and the evidence is extremely weak and poor. "Dear" is pronounced "Deer" in English, and no one pronounces it "Diar," except maybe a small child or some kind of boor.
You're confusing devils and demons; devils are small and flit around, while a demon is a demon.
Don't you think that such phrases are typical of the atmosphere of these games?
There's a Buddha (!!!) depicted there, what kind of eye?! I've read about Shintoism and can distinguish between an image of Buddha and a Hindu statue, but you apparently can't. Don't confuse Hinduism and Buddhism!
It means that he wants to destroy the world; there's nothing about the confrontation between light and darkness.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!