In a world where humanity is intertwined with aliens, a trio of young adolescent girls are elected for alien fighting as they are forced into growing up with symbiotic life-forms.

Otani Yuri, much to her disgust, has been elected by her class for alien fighting duty. Together with Tonime Kasumi, who joined the alien fighter simply for the sake of doing so, and Kawamura Kumi, who became and alien fighter to avoid the responsibility of yet another year of class presidency, she must defend her school from periodic alien attacks. Introspection, fear, anxiety and friendship await Yuri as she is forced to stare life itself in the mouth in her chaotic coming of age.