In the shadow of modern Japan, tengu are not creatures of legend but real monsters formed from the malice and ill will of humanity. Those who wield blades to cut down these spirits are known as Tōbatsushi, or sword punishers. The story centers on Akari Hinomiya, a boy raised on a remote island who carries within his heart the soul of Hajun, the most vicious and powerful great tengu who once nearly brought the world to its knees.

As a first-year candidate at the Karasuma High School for Tōbatsushi, Akari struggles to control the immense and often unpredictable power surging inside him. He is joined by his older brother, Haruto Hinomiya, a naturally gifted fighter who acts as a leader for the younger students, though he is haunted by his duty to stop his own brother if Hajun ever awakens. Their classmate Ushio Kiryu, who lost his family to a tengu attack as a child, burns with a deep hatred for the monsters, a resentment that often turns him against Akari for harboring a tengu's soul. Another student, Inoririn Kyokane, presents a cynical and indifferent facade, preferring to skip training, though she possesses a sharp mind and a hidden kindness that helps balance the volatile group.

Their battle is not only against roaming spirits but also against the influence of Kurama Tengu, one of the great tengu leaders who acts with mysterious amusement, observing the chaos of human folly. As the series progresses through its side stories and main narrative, Akari must confront his destiny, navigating the fine line between using Hajun's power as a weapon to save his friends and losing himself completely to become the disaster the world fears.