Rin, is a seemingly normal high school girl. However, on her 16th birthday, her life changes forever when her house is stormed by government special forces who brutally kill both her parents. Just then, dormant mutant genes in her body take over, transforming her arm into sharp claw which she instinctively uses to slaughter the soldiers. While attempting to flee her hometown, she comes across a group of girls who were also born with mutations. They call themselves “Hiruko” and claim that their kind have lived in Japan far longer than normal humans have. Each girl has the ability to transform parts of their bodies into deadly weapons. Together they form a team and train to one day take revenge against the Japanese society that has been persecuting them for centuries.