This prologue episode is a slightly more personal story, showing an incident that built the deep bond Tatsuya and Miyuki share with each other. It, however, still suffers from all the pacing and plot issues from the main series – escalating in an insane manner and not doing anything to de-stupify the core premise of the show... Maybe even worse, as the explanation it gives for Tatsuya's treatment is beyond stupid and makes the whole magical aristocracy of Japan look like even bigger morons than before.
The one thing this special does better than main seasons of the show is exposition – there are fewer clunky info dumps and while the whole arc is arguably rushed, it at least doesn't include pointless downtime. In the end, it's just more content for fans of the main story – nothing less and nothing more.
