For their silver anniversary, Vanilla and Coconna return to Uoodo along with Gotho in the hopes of reuniting with Chirico. Once there they find a red shouldered AT at the Battling arena.

The story of the anime is set in the year Mobile Century 8013. It has been over seven millennia since humanity was wiped out on Earth, but the surviving military robots continue to wage war with no end in sight. The war has embroiled the Rebellion Federation that controls Europe and the Principality of Shin centered in Asia. Three young robots stand up to put an end to this futile war. (Source: ANN)

To save the Earth from alien invaders and their giant monsters, Dr. Kishida does what any other red-blooded mad scientist would do: he builds a giant robot—the ultimate feminine fighting robot! Unfortunately, his grand-daughters refuse to pilot it! Apparently, they've got more important things to do than becoming teenage super-heroes. Besides, how are you supposed to study for your college entrance exams while getting beaten-up in battle? Fortunately for Dr. Kishida, things aren't too well for the invaders, either. According to their reports, the Earth was the perfect target: lush, peaceful, and relatively defenseless. Theoretically, the planet should've surrendered long ago. Now, the war is at a standstill, the dreaded Accounting Department is warning about the serious cost overruns, and the head of the home office has arrived from Galactic Headquarters to personally oversee operations. Has Headquarters decided to unleash, The Audit—or do they have something even more evil in mind? The fate of the world rests upon two people: Aya Kishida, one of the doctor's granddaughters, who may have to give up prep school to pilot the mighty (and lovely) ARIEL; and a mysterious alien named Saber Starblast, who may have the power to defeat the invaders once and for all...

According to Kadokawa, an OVA of R-15 will be bundled with the tenth volume of the novel.