Unknown attackers have invaded Earth and conquered it, forcing mankind to retreat. Nevertheless, hope remains in the form of extraordinary schoolgirls with superpowers. At schools like Shinjugamine Girls Academy, Star Guardians learn to defeat these attackers alongside regular academic work. This life-saving duty is taken seriously by members of the Shinjugamine Hoshimori troop, including first-year student Miki Hoshitsuki. Despite being average girls who gain magical abilities from a special tree, they still have to deal with everyday challenges. However, with the arrival of a new recruit, danger and urgency now dominate their heroic responsibilities.