Yuusha ga Shinda! opens in a fantasy world where the Gates of Hell have reopened and demons once again threaten the land. Touka Scott, an ordinary villager who lives quietly tending his radish farm, is dragged into the crisis when a demon attacks Yuna Eunice, his childhood friend. Just in time, the legendary hero Sion Blandan arrives, saves Yuna, and drives the monster back. The relief is brief: Sion later dies after falling into one of Touka's traps, which were meant to protect the farm.
To keep the world from collapsing without its champion, Anri Haysworth, Sion's necromancer companion, transfers Touka's soul into Sion's corpse and brings the hero back in an unusual new form. Suddenly forced to inhabit the body of the legendary hero, Touka must live with Sion's reputation while taking on the dangerous mission of resealing the Gates of Hell. With Yuna and Anri at his side, he faces demon attacks, a world thrown into confusion, and the absurdity of his new position as he struggles to protect peace and survive a role he never wanted.