A "Brain" is discovered in a region of Japan and an disposal mission is ordered. It ended in a huge massacre. A new elite unit is then called to deal with this threat. It's the unit "5121", consisting of young men and women. A new mysterious rookie also happens to lend a helping hand.

It's finally summer vacation. Unfortunately for our young warriors, they do not have the right to take time off. Yet they will celebrate a sad anniversary of the death of Akane, a former fighter who died in combat. Hayami remembers this sad event and is going to meet the beautiful May, which also assists at the ceremony.