"G-On Riders" is a 12-episode anime series that blends elements of science fiction, action, and comedy. The story centers around a group of high school girls who are recruited to pilot advanced mecha units known as G-Forms to protect Earth from an alien threat. The narrative unfolds at the prestigious Seigaku Academy, where the protagonists—Ruriko, Ayaka, Misa, and Chihiro—are ordinary students until they are chosen by the mysterious organization GARDA to become the titular G-On Riders.

The alien antagonists, known as the Raika, seek to invade Earth and harvest its resources. The G-Forms, powered by a unique energy source called G-Power, are humanity's only defense against the Raika's advanced technology. Each G-Form is tailored to the personality and abilities of its pilot, with the mecha transforming into various configurations to adapt to combat situations. The series explores the girls' growth as they balance their responsibilities as defenders of Earth with their everyday lives as students.

Ruriko, the de facto leader, is determined and resourceful, often taking charge in critical moments. Ayaka, the most athletic of the group, brings a competitive edge to the team. Misa, the brains of the operation, provides technical expertise and strategic planning. Chihiro, the youngest and most innocent, adds a touch of humor and emotional depth to the group dynamic. Together, they face increasingly dangerous Raika attacks while uncovering the true motives behind the invasion.

The plot progresses through episodic battles interspersed with moments of character development and school life. As the series advances, the girls discover that the Raika's invasion is tied to a deeper conspiracy involving GARDA and the origins of the G-Forms. The final episodes escalate the stakes, culminating in a climactic battle that tests the team's unity and resolve. The series concludes with a resolution to the immediate conflict while leaving room for potential future developments.