What’s here belongs neither to us nor to the demons. it’s only a form of a much greater and purer magic. it can do harm in the hands of the wrong man and lash back on him, but the superior man need not be afraid. i need to know the meaning

My understanding/translation of this would be just basically saying that the world we live in (assuming that's what "here" is referring to) is controlled by an almighty being that is above us and the evil that exists here. If controlled by a lesser being, it can do harm to him. Assuming that this is because men (humans) are seen as weak, and naive compared to almighty beings.

However, this last part is a bit tricky. The speaker could be referring to a man smarter than another man whose desire is to control the world, or they could be referring to an almighty being.

This is just my interpretation of the statement, there's no way of knowing what the writer intended for this to mean, unless you asked the writer himself! I also don't know the context of the story so your guess ought to be better than mine. But anyway I hope this at least gave you an idea of the interpretation :)

That’s nice! sounds really fun.