The setup sounds like filler until the Black Knights show up and the entire island's fragile peace collapses in minutes. Meliodas imprisoned and powerless while everything he just met burns is the kind of cruel timing this series lives for. The movie understands that the Sins are strongest when they're separated and desperate, forced to claw back from nothing, and that's exactly what it does to them.

Meliodas and the Seven Deadly Sins venture into a remote land hunting for a legendary ingredient: the sky fish. Along the way, Meliodas and Hawk wind up in the Sky Palace, a realm above the clouds where every inhabitant has wings. Because he resembles a local criminal, Meliodas is arrested and thrown into prison. Meanwhile, the residents are readying a ceremony meant to guard against a ferocious beast that awakens once every three thousand years. Their preparations are upended when the Six Knights of Black, a ruthless Demon Clan army, arrives and breaks the seal on the monster, putting the lives of the sky dwellers in danger. As the Sins and the winged Celestials join forces against the invaders, the battle will decide whether the Sky Palace survives.