Ever since the death of his father, the burden of supporting the family has fallen upon Tanjirou Kamado's shoulders. Though living impoverished on a remote mountain, the Kamado family are able to enjoy a relatively peaceful and happy life. One day, Tanjirou decides to go down to the local village to make a little money selling charcoal. On his way back, night falls, forcing Tanjirou to take shelter in the house of a strange man, who warns him of the existence of flesh-eating demons that lurk in the woods at night.

When he finally arrives back home the next day, he is met with a horrifying sight—his whole family has been slaughtered. Worse still, the sole survivor is his sister Nezuko, who has been turned into a bloodthirsty demon. Consumed by rage and hatred, Tanjirou swears to avenge his family and stay by his only remaining sibling. Alongside the mysterious group calling themselves the Demon Slayer Corps, Tanjirou will do whatever it takes to slay the demons and protect the remnants of his beloved sister's humanity.

In the wake of defeating Boros and his mighty army, Saitama has returned to his unremarkable everyday life in Z-City. However, unbeknownst to him, the number of monsters appearing is still continuously on the rise, putting a strain on the Hero Association's resources. Their top executives decide on the bold move of recruiting hoodlums in order to help in their battle. But during the first meeting with these potential newcomers, a mysterious man calling himself Garou makes his appearance. Claiming to be a monster, he starts mercilessly attacking the crowd.

The mysterious Garou continues his rampage against the Hero Association, crushing every hero he encounters. He turns out to be the legendary martial artist Silverfang's best former disciple and seems driven by unknown motives. Regardless, this beast of a man seems unstoppable. Intrigued by this puzzling new foe and with an insatiable thirst for money, Saitama decides to seize the opportunity and joins the interesting martial arts competition.

As the tournament commences and Garou continues his rampage, a new great menace reveals itself, threatening the entire human world. Could this finally be the earth-shattering catastrophe predicted by the great seer Madame Shibabawa?