A world where the authority of law has collapsed and crime and terrorism have become daily life. When public power alone could not maintain public order, the private armed organization Resistance was born to protect the people.

Siblings Reika Shimamoto and Guest, who lost their parents as children, lived relying on each other. However, when Reika was 17, chaos broke out due to a subway bombing, and she lost hold of her only brother Guest before her eyes. In the despair of not even knowing if he was alive, Reika joined the Resistance with a vow never to lose a loved one again.

Four years later, Reika, now 21, becomes the Captain of the 1st Squad in recognition of her outstanding skills. And one day, while in charge of interviewing new members, she stops breathing when she sees the applicant who opens the door and enters. Standing there was her younger brother, Guest, whom she thought had died long ago.