Rin Okumura is always picking fights with delinquents unlike his more studious younger twin brother Yukio Okumura. He is surprisingly hired for a part-time job but gets fired after he encounters a hobgoblin that wreaks havoc in the store, and is grounded by his father. The next day, he encounters a demon that causes his dormant demonic powers to awaken. His guardian, Shiro Fujimoto, saves Rin and reveals that he is the son of Satan born from a human.