I have to deduct several points on behalf of whomever shoved 33 minutes of footage from the 3 seasons into a poorly edited and haphazard mess. I feel sorry for everyone who's been baited into buying a movie ticket for this, when in reality it's a decent OVA with a bunch of rehashed footage in the front to make the runtime movie length.
Given this is titled "Prelude" I find it very dangerous for people who decided to start this story here. There's massive spoilers to the main story without warning in the recap, and it entirely expects you to know so much context before seeing it.
This is a poor excuse for a cash grab, even by Japanese Marketing standards.
This is a shame too, as the OVA is actually a nice story once you finally get to it.