In a bleak near future where humanity succumbs to the viral parasites called Gastrea, a boy named Rentarou resides in a small territory near Tokyo, part of the 'Civil Security' group fighting these monsters. Alongside his partner, the young and talented Enju, they use their unique abilities to tackle dangerous missions. Their routine changes when a covert government task lands on their laps—to save Tokyo from impending doom. Embark on this gripping tale of heroism and action as they strive to protect their city from destruction.