A guard is about to execute the bound “woman” when the group of youngsters intervene.
After her release, she proceeds to hunt the boys down with a bow and arrows.
Some of them manage to escape her prison.
Her identity as a demon is revealed when somehow her muzzle is removed.
The guards turn out to be the good guys, demon-hunters who destroy demons when they manage to enter the human world.
They were also guarding a gate to hell.
It looked like a crater in the ground, maybe in a forest.