Teenager Asumu Adachi is at a crossroads. He's about to start high school and unsure of what he wants to do with his life. And as if puberty & homework weren't bad enough, he stumbles upon a huge secret: his new friend Hibiki is secretly an oni! Hibiki & his oni comrades are the only thing stopping the monstrous Makamou from devouring mankind.
As Asumu is pulled into a secret war, Hibiki & his allies teach the teenager what it means to be an adult in a uncertain world.
The Kamen Riders, known as OniIcon-wikipedia, 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 raise of Makamou numbers proves to be a prelude to an upcoming calamity.