The story revolves around 15-year-old Rin Okumura, who, along with his younger twin brother Yukio, was raised by Father Shiro Fujimoto, an Exorcist. One day, Rin learns that he and Yukio are the sons of Satan. Witnessing Shiro dying to protect him, Rin draws the demon-slaying sword Kurikara, which restrains his demonic powers. From that moment on, Rin not only gains demonic features like fangs and a tail, but also the power to ignite into blue flames that destroy almost anything they touch.