It sums up the basic plot and storyline of the series, refreshing the viewer's mind with everything that has happened up to episode 17. There isn't much to say about this: it has the same good voice acting and songs from the series, together with the same art style. Character development is fairly explained in this summary, too. The story of the series itself is outstanding, but in this recap they omit too many interesting scenes and twist of events that keep you in suspense while watching the real series.
It's not necessary at all to watch this. You've seen every scene of this recap in the real series. Actually, you might get bored re-watching it in this manner. Even so, it synthesizes the storyline fairly well.
