The only thing I didn't like was that there seemed to be some plot discontinuity between what I believed was episode 2-3 or 3-4 somewhere around there.
also plot hole if yuki's world was the one under attack why couldn't they just escape to a different world to begin with. Like the world they end up in, in the end the whole pitfall to hell said it would consume "the world" but it never specified which world and there were clearly 7 of them created one for each fragment.
Another thing was that if you were paying at some point earlier in the episodes the girl talking about her homeland said something like "the witch betrayed Verard" or something to the effect of that and for me that was enough for me to guess that the witch trapped in the crystal was betraying the main characters into killing off the black knights who were probably good guys in the first place, but I'm usually pretty quick on picking up the plot of shows and figuring out where they are going...