The prologue consists of a 25-minute recap of the series.

It is linked to the main movie, so by playing it you will see the movie as it aired in Japan, with the recap prior.

You can also play the movie file individually to just see the movie alone.

This linking feature makes use of ordered chapters which may not work in some players such as VLC.
In this case, it is suggested to simply play the files individually, or better, download a player such as MPV (suggested) or MPC-HC.