OK, this is it, a war started between two human cultures while humanity is fighting a war against demon (who turn out to be from another world INSIDE their own) and the Hero apparently has to fight the Demon Lord (who got possessed by, at least one of, the spirit of previous demon lords). 'Till that point, she (yes, I said "she") was a more intelligent (and genre savvy) ruler who (strangely enough) seeks to not 'rule' the world but rather 'save' the world...with the Hero's help of course.
And, no, it's not that I'm not bothering to remember their names. The characters in this series are seriously referred to by their titles rather than names, even when they technically have more than one. The Demon Lord and the Crimson Scholar are actually the same person (even though there is a point where the elder of the Maid Sisters poses as the Crimson Scholar), same thing with the Hero and the Black Knight.
Let's do our best to see the other side of that hill..
Warning!: This post contains spoilers if you haven't seen the entire series yet.