Available to watch via Netflix. The more I thought about the movie, the more I realized that it had potential to be much more than it was. I'm not saying it was bad by any means; lately anime movies have not been living up to the series from which they came. "Prisoners of the Sky" is an interesting and amusing movie, but nothing really out of the ordinary. The timeline is somewhere in the "Revival of the Ten Commandments" season.
A case of mistaken identity; as Meliodas (and Hawk) are looking for flying fish to prepare for Bartra's birthday (while the other Sins gather ingredients as well), they come across a lake/pond with a strange glow. Upon looking under the "water", they see dozens of flying fish and jump right in, only to find themselves somewhere completely different where Meliodas is mistaken for a boy who looks just like him who had supposedly ran away from his duties.
As Meliodas deals with the case of mistaken identity (or lack of deals with it), the boy who escaped meets up with the other Sins and since Meliodas is involved, they decide to help him out.
The entire gang is there: Meliodas, Elizabeth, Ban, King, Diane, Gowther, Merlin, and Escanor. Hawk gets mistaken for a savior, and even Hawk's Mama has time to shine. Everyone remains in-character, though they are very much overqualified to save the day in this case.
Solaad - A boy who looks near identical to Meliodas with a few key exceptions: His eyes are blue, and he has wings. He is also more timid and unsure of himself (the Sins knew almost straight away that he wasn't their Captain; Merlin in particular).
Ellatte - Solaad's fiance and a Celestial who looks nearly identical to Elizabeth with only a few minor differences (which, of course, Meliodas realized immediately). She is outgoing and has a bit of a temper, and is willing to fight against anything, even demons, which threaten her and her people.
Solaad's Father - The king of the Sky People, he hopes for Solaad to become a great warrior and be able to wield the Sacred Sword which only the "chosen" of the sky people are able to wield.
If you've seen "How to Train Your Dragon", Solaad's father will probably remind you of Hiccup's father almost straight away, even down to one of the lines. Just wanted to throw that out there in this more subjective section.
No complaints about the music and animation; the ending song is nice, and we get to hear "Perfect Time" again during the final battle.
Speaking of battles, that's where this movie falls short. None of the fights were that interesting, especially compared to the high-stakes fights in the Nanatsu no Taizai series itself. Even when "Perfect Time" kicked in as they were getting ready to thrash the final "boss", it just didn't feel as...intense. The way that combat was ended certainly was cool, there's no doubt about that, but everything which led up to it was just sort of...too easy.
None of the Sins struggled against their opponents, and if it wasn't for Solaad's father showing up and interfering with the fight then even Meliodas wouldn't have had a problem with the boss of the bad guys. Due to that, none of the fights felt "epic" or even very interesting. The Sins were far too overpowered; Meliodas absolutely wrecked one of the bad guys in a split second without even going into his demon form, for example.
Getting to see Merlin fight was a treat (as we've only seen her fight once before, and it wasn't as drawn out), and I don't think anyone would expect her to struggle against an opponent after seeing what she did to one of the Commandments.
Still, the fights left a lot to be desired. Even the battle against the "final boss" was sort of a "what?" moment as it became a creature that those who read the manga will know more about (as the anime has yet to touch upon them). Knowing that, it makes sense that the Sins start to struggle against the thing, but even that struggle was sort of just...not very engaging.
The movie has a lot going for it in terms of comedy (like seriously, whose idea was it to let Meliodas cook for the King's birthday?), but there were a lot of issues all around besides that (honestly, how did the father not realize that Meliodas wasn't his kid? Meliodas even said he wasn't). Other story issues I won't go into because they'd contain spoilers, but it brings be back to something I've always wondered even in the series itself (how some demons managed to escape the sealing of 3000 years ago, for example) as well as the wishy-washy motives of the antagonists of the movie.
The trailer makes it look much more "hyped" than it actually is. Again, it wasn't bad, but just don't expect riviting battle scenes or clashes on a level of Meliodas vs Hendrickson. I'd even go so far as to say that the Sins' first clash with Guila was more interesting than any of these fight scenes.
That said, it is worth watching if you're a fan of the series. It had potential to be more, but I feel like that wasn't really grasped. Some of the best scenes are ones where characters like Ban and Elizabeth encourage Solaad due to the boy's lack of confidence. In terms of scenes like that and comedy, it works very well. In terms of the antagonists and fight scenes, it could have been much better.