The Kamen Riders, known as Oni, battle man-eating beasts called Makamou with "pure sound". One of the Oni, a man named Hibiki, ends up having a "teacher-and-apprentice"-like relationship with Asumu Adachi. A young boy unsure of himself and is at a crossroads in his life as he transitions to high school, Asumu learns to be an adult through watching Hibiki and the other Oni as they all train together to hone their skills in fighting the Makamou and the homunculi aiding them. However, the sudden rise of Makamou numbers proves to be a prelude to an upcoming calamity.