Sixteen years have passed since a mysterious alien ship crashed on Earth. Graviton City, once leveled by the ship's crash, is now a bustling metropolis. Within the city's high school, superhuman high school student A-Ko Magami dukes it out with the diabolical genius B-Ko Daitokuji, who will stop at nothing to win the friendship of A-Ko's buddy C-Ko Kotobuki. Meanwhile, in outer space, another alien ship is on course towards Earth to find its planet's lost princess.

[Source: Anime News Network]

Three weeks after the incident that left Captain Napolipolita's ship balancing on top of Graviton City, A-Ko and the gang go on summer vacation. While A-Ko ponders losing some weight and B-Ko devises another plan to defeat her redheaded rival to win C-Ko, Napolipolita and Spy-D experience severe homesickness - begging for a way to return to their home planet. Meanwhile, Hikari Daitokuji - B-Ko's father and the CEO of the Daitokuji Financial Group - arms the local military with new mecha to attack Napolipolita's ship and obtain its advanced technology.

[Source: Anime News Network]

In the middle of another break from school, A-Ko dreams of finding the perfect boyfriend. Because of this, she and C-Ko get into an argument that leads to C-Ko running away and nearly getting hit by a motorcyclist named Kei. While working part-time at a fast-food restaurant to raise money for a party dress, A-Ko meets Kei and immediately falls in love with him. B-Ko happens to like him as well; however, both A-Ko and B-Ko are unaware that C-Ko is the apple of Kei's eyes.

[Source: Anime News Network]

In Iraq, a group of archaeologists discover ancient relics that prophecize the coming of a superior race and the end of all civilization. Meanwhile, back in Graviton City, as A-Ko and B-Ko's rivalry over Kei intensifies, Mr. Daitokuji sets up an arranged marriage between Miss Ayumi and Kei. Furious over the engagement, both A-Ko and B-Ko do whatever it takes to prevent the wedding from going through. Little do they know that another alien fleet is on its way towards Earth.

[Source: Anime News Network]

A-ko and B-ko are bounty hunters in an untamed world. When a young heiress, C-ko, falls out of the sky and into their hair, they find themselves battling space pirates and galactic police. Turns out the high-pitched, hungry C-ko holds a secret—the spirit of an ancient evil—and is the center of a plot to destroy the universe!

[Source: MyAnimeList]