I have added templates to the top of each article in question in an attempt to appease him. With the exception of Demon Beast Attack Arc, that is admin protected - I don't see any particular reason why, though.
They were here even before I started editing on the wiki. But as I am part of the new management, my personal decision would have those pages removed and have the user that copied the translations aptly punished.
Thanks for putting that plagiarizer's articles into categories. Although it would be more helpful if it were a subcategory of Category:Light Novel and not the spelling variation Category:Light novel. They are not case sensitive.