Look at the Pretty Butterflies

An outbreak of a virus has been going on for quite a while but nobody thought that it was deadly since they thought simple medicine will get rid of it. But when Akira goes to school one of the students goes insane in the middle of class and starts attacking everyone. Soon a group of soldiers start taking people that haven't been affected by the virus and Akira is one of them and has to now live in a world that is slowly collapsing while trying to protect her little sister.