This world has been invaded by bugs.

With the appearance of the "Armored Bugs," mutating insect monsters that can overcome all modern weapons, humanity has been robbed of much of its living space. The only ones who can stand against such adversaries are the "Noble Butterflies," girls who harbor "Insects" that have gone through evolutions differing from the armored bugs.

One of the candidates to become a Noble Butterfly, Odamaki Ayumi, still suffers from the fact that she is unable to become one. Her best friend, who was supposed to be with her and was her object of admiration, has left her and no longer seeks her company.

Those days of despair came to an end when she was on the verge of death in a battle with armored bugs.
"Don't think that I... will die without doing anything!"

With the end near, the girl's body transformed into a butterfly one. And the flapping of her wings will bring about a revolution in the world...!