Spoiler-free review

After three seasons of almost nothing but slice-of-life and loli fanservice pandering, Prisma Illya was getting a bit stale. Luckily, the fourth season was much more plot-focused and was a nice set-up for this movie, which fills in a lot of the backstory that the show is based on. Oath Under Snow answers a lot of questions you might have had regarding this new Holy Grail war and how exactly Miyu came to be a part of it.

Within the first few seconds of the film you can already notice the change in quality compared to the show. That's one thing I love about anime movies, they always have that layer of polish on them that really captures your focus. There is a somber feeling throughout the movie that sets the mood very well. The world that the characters are in does not have much time left, and the main character, Shirou, is stuck with an uneasy feeling for the unknown future.

That uneasy feeling instantly turns into dread when the fighting is put into motion. Shirou is suddenly thrust into the middle of a war when the last thing he has to live for is taken away. The fight scenes are solid. There weren't many but the first major one in particular was extremely tense and played out well. Each fight had a strong soundtrack to go with it which further amplified moments of silence.

Something I'd like to point out is the voice acting. To put it simply, it's really fucking good. Across the board, all the VA's did such a good job portraying their characters that I'd say it's probably the largest strength of the movie. The emotions brought out by the VA's really made the characters that much more enjoyable and real.

As a final note, I appreciated how this movie makes a lot of connections with the anime that explain Miyu's actions and feelings that she showed during the earlier seasons of the show. little details from the show were pointed out to be more important than what was previously thought. It did a good job at filling in all of the gaps in Miyu's story which in turn made me like Miyu's character a lot more.

TL;DR: This prequel movie fills in the backstory of Prisma Illya, as well as Miyu and Shirou's story. The fight scenes are good, the voice acting is great, and if you've watched the first four seasons of Prisma Illya then obviously you should watch this movie too.