A bike action that depicts the activities of Kosuke Katayama, also known as "Sepahan," who drives his brother's keepsake bike Mach III. Kosuke Katayama, a high school student called Sepahan, manages the bike Mach III of his late brother Shinji, who was the legendary head of a runaway tribe, with exquisite techniques. One day, Sepahan, who is worried about his sister Maki who went to a runaway rally, skips Mach III and gets into a coffee shop where Maki should be ...!?