In AD 2045, a group of military cadets, attending the preparatory course of the Central Military Academy, proceeded for training aboard the space station Aries. Within this group of cadets were Ryota Aizawa and his classmates including Sayaka Nagase and Kazuhiko Nitta. The situation went sour when a terrorist group called "Jararacas" took over the station. While the military successfully evacuated the station, Ryota and his group were trapped aboard. Worse still, the boarding assault left most of the military forces dead, effectively leaving the cadets on their own.
An unexpected twist occurs when a mysterious virus was released within the station, gaining control of almost all personnel and turning them into mindless creatures in the process. This forced everyone, friend and foe alike, to find a way out of the station alive.

(Source: Wikipedia)