Labeled as a delinquent and bad influence, high school student Kyosei Ichinose choose to stay out of the people around him, indulge himself to his headphones, pick fights against other people and stay alone. He was later famous for being a dangerous fellow that even his fellow students and his teachers feared him. One day, everything is normal until the world is now in turmoil after the appearance of a mysterious disease that turns humans into mindless cannibals, infecting humans all around the country in an alarming state. After receiving a distressed message from his former friend, he reluctantly returned only to find the school overrun by the dead. Armed with his house keys, a revolver and a duffel bag containing a few items to aid the rescue, he returned to the school without knowing why he still need to rescue a former friend.

The sweet temptations of sin, always brought him back for more. Once he tasted the forbidden fruit, his will to do wrong always overpowered his ability to do right. Is it because of his haunting past? Or is it the terrifying thought of his unknown future? Ironically his name is Sin, or so everyone thinks. However, when a courageous, feisty, and sexy woman is added into his life during a mission, his way of living is completely flipped upside down. Xena's curves, smart mouth, sensuality, and sweet and loving personality slows down his indulgence in the forbidden apple. But, is her love enough to stop from him from sinning completely?