It's an animated short to celebrate PreCure's 5th anniversary, which played in cinemas before the start of Yes! Pretty Cure 5 GoGo!: Okashi no Kuni no Happy Birthday!. It's simplistic, dumb and lovely.
It's the first All Stars movie, teaming up all PreCures to date. (What's more, it's canonical. In later All Stars films, the girls here aren't as surprised as everyone else to meet the other PreCures.) Also, by All Stars standards, the line-up is tiny:
FUTARI WA (3) = Honoka, Nagisa and Hikari
SPLASH STAR (2) = Saki and Mai
YES! (6) = Nozomi, Rin, Urara, Komachi, Karen and Kurumi
Over half of those are the Yes! PreCures. Anyway, they're attending a concert... but the stadium's empty! Instead, they meet a giant monster. Everyone transforms into their PreCure identities, then is surprised to find that they're not the only people doing so. (Nozomi's bewildered head turns made me laugh.)
What happens now? Well, obviously a FIGHT!!! (This includes iconic shots lifted from the different PreCures' title sequences, not just the obvious ones from Futari wa but also a big hero charge for the Yes! girls.) Their opponent must be fearsome, if you consider how much damage it takes without falling over, but then the combined PreCures hit it with all their finishing moves at once. (Yes, this includes Nagisa and Honoka's, ahem, Marvellous Screw.) That does it.
Next is the silly bit. The stadium/coliseum fills up with people and...
"We've got to dance!"
What? Why? Who told them? Well, never mind. We now get an endearing but badly animated All Stars dance sequence, which started a tradition and is unique for two reasons. Firstly, it's hand-drawn. After this, they'd all be CGI. Secondly, it's the only time they'd dance in their civilian clothes, not their PreCure outfits.
If you're unfamiliar with PreCure, you'll think this is codswallop. The rudimentary plot is about right for a five-minute short, while "we've got to dance" is unintentionally hilarious. Personally, though, it made me happy. It's got iconic music, attacks and visual quotes. I've seen all the PreCure series to which it's paying homage and it's a love letter.