While the magical girls of the Corona House crew are out on patrol one evening, they're treated to a most unusual sight—a Sanae they don't know falling from the sky! Just who is this third Sanae, and what is her story?

Koutarou and the girls have kept Earth, Forthorthe, and Folsaria safe thus far by driving back evil after evil... But the threat lurking in the shadows now is unlike anything they've ever faced before. Will they still be able to defend themselves and everything they hold dear when the stakes of the battle they've been fighting shift significantly?