This OVA provides so much foreshadowing and insight into Mikasa Ackerman as a character, as well as the curse that is her love for Eren Yeager, even in a world where cruelty doesn't happen to her, she can't save Eren. The idea that the Mirror Man is a reflection of her future self trying to provide Mikasa with the strength to move on is very significant, given what we learn near the end of the manga in chapter 138, which is one of the best chapters in Attack on Titan, just like this is the best OVA in Attack on Titan, and I'd argue all of anime.
