Gate Keepers 21

Ayane Isuzu destroys some Invaders, and collects the crystals they leave behind. While looking for more Invaders, she sees a girl fly across the sky. After school the next day, Ayane meets with a mysterious man who tells her to locate a girl called Miu Manazuru, for she is a Gate Keeper. Ayane gives the man a bag of crystals in exchange for money. That night, Ayane approaches Miu, and tells Miu to join her in her effort to destroy the Invaders. Miu is wondering what to do, when they are suddenly surrounded by Invaders...