Originally Posted by
Cymmina
You really didn't pay attention to the AF story, because it's all there. The Crimson Grimoire is what happens when a Grimoire like we normally have is infused with the blood of mages, specifically, the blood of your colleagues. That's why we can't have it (murder is bad and all). I would guess the Crimson Grimoire is what gives stratagems the behavior you see in the AF3 fight.
As for Gunther, his identity is explained in the G5 fight. There should be a youtube video of it somewhere that you can watch.