Season 1

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...

Ayane and Miu are chasing after a truck under control of the Invaders. Ayane manages to throw off the police that were following, and then tells Miu to fly over to the truck. Miu almost succeeds, but hits a highway sign instead. The next day, Miu and Ayane are at their school, when they see what appears to be a ghost. They decide to follow it, and in the process stumble upon an elevator that takes them to an underground complex. Down there they discover something that can help them find the Invaders.

Miu's school friends notice that Miu seems distant depressed. Miu's friends decide to take her to a karaoke lounge to try to cheer her up. They are in a singing room when an interruption occurs in the form of a power outage. Suddenly, Invaders start swarming all over the place. Ayane hears about the Invaders at the karaoke lounge, and goes to help.

A new Gate Keeper, Satoka Tachikawa, has appeared. She destroys Invaders to collect their crystal remnants for money. Ayane and Miu are outside of school when Satoka confronts them. She attempts to get Ayane to answer a question about her past, but Ayane manages to slip away. Later, Reiji notices signs of Invader activity, and Satoka rushes off to fight them.

Miu's decides to visit Reiji at his headquarters, where they talk more about the Invaders, and Ayame.

The Gatekeepers face their final confrontation against the Invaders.