This is Fate/Zeros version of the Tiger-Dojo from Fate/Stay Night. As such it explains quite a bit of background-information, both on the war in general and on certain servants. While this is mostly lighthearted fun (“you snuck in all proud of yourself just because a cool-sounding Kajiura theme was playing”), there soon starts to be an increasing amount of weirdly dark scenes. And while Irisviel seems to be quite nice for the most part, some of her decisions become questionable...
All of this would already be quite nice, but the thing that really turns this into more than just an explanatory series is the absolutely magnificant second halve of the last episode which takes a sudden turn into a MUCH darker direction.