Sumire Takahana was a once normal high school student, until one day, she picked up a mysterious brooch and began to see soul-eating demons known as Virus. Now under attack, Sumire was saved by the owner of the brooch, Lucia, and Lucia’s Vaccine-loaded gun. However, instead of shooting the Virus, Lucia accidentally shot Sumire herself, turning her into a living antivirus. Together, Sumire and Lucia will try to uncover the secrets of the Virus before they devour all of humankind.