60 years ago, a wealthy and powerful organization called Saint Corp. sponsored a group of eccentric and mad scientists to conduct experiments and researches on creating super humans for military purposes and black market bidders. However, the experiments went deadly wrong and caused explosions of toxic gases and chemicals. These gases spread out to towns and communities near by and infected the entire population of the whole region. As last resort, Saint Corp. quarantined the infected area and burnt it down the ashes and sealed the area with sorcery.

In order to cover up their messes and distract attention, Saint Corp. built a martial style school over the central experimental area--RAN Academy. They also established towns and business districts in rest of the region. Quickly, people and the rest of the world forgot about the terrible incident as the towns and commerce of the region grew and prospered.

Due to the regional success, RAN Academy became top ranking school and parents from all over sent their children to study there. Aside from regular curriculums, the students participated in extracurricular activities and trained as Fighters, Swordsmen, Archers, and Sorcerers.
One day, a group of dare-devil students went on exploring the academy campuses as they heard an urban legend about the academy being a military base in the past. They sneaked around Leonine Campus, the campus of the east, and found a hidden underground sewage tunnel. However, their curiosity and recklessness caused the breaking of the Saint Corp. seal and the deadly toxic gases and chemicals to leak out once more. The campus of Leonine fell and all the students on campus were infected by the gases and chemicals and mutated into monsters, zombies, or creatures unimaginable. Soon, the infection spread to towns and districts as people got in touch with the infected students. Surprisingly, the rest three of the academy campuses--Sacred Gate, Mystic Peak, and Phoenix, remained uninfected and healthy due to protective borders and charms set up by Saint Corp. when they built the academy.

In order to stay uninfected and hope to rescue their family and friends, the students of each healthy campus ganged up and went on hunts for the sources of the mutation and destroy them once for all. It's survival for the fittest indeed!