The Hikari Girls Earth Defense Committee, abbreviated as SHAM, is formed with the singular goal of searching for aliens who have come to invade Earth. Their primary strategy involves first locating the extraterrestrials' UFOs. However, their efforts prove largely unsuccessful, and their increasingly disruptive activities, which end up involving the entire student body, become far more noticeable than any actual progress. The chaotic yet ordinary committee activities of these otherwise typical schoolgirls escalate dramatically when a mysterious girl claiming to be an alien appears before SHAM.

The story is set within a girls' high school and centers on the members of the SHAM committee. The narrative arc of the first volume follows the committee's loud and fruitless searches for a UFO and their subsequent encounters with the self-proclaimed alien girl, leading to even greater pandemonium. In the second volume, a rival group called the Yuuaidan appears. These girls seek to escape a polluted Earth, placing them in direct opposition to SHAM's mission to defend the planet. What begins as a high-stakes conflict over Earth's future devolves into passionate discussions about UFOs, forming the core of the second volume's storyline. The series concludes after two volumes.