Katsumi Yuuto, mistakenly summoned as a hero to defeat the Demon King in another world, lands in the world of Astoria as a regular person without receiving any power from the goddess. However, the Remiel Kingdom, which failed in summoning the hero, fears the condemnation from all over the world and decides to treat Yuuto as the hero.

Forced to fight as a hero, Yuuto, in the midst of battle, witnesses his beloved childhood friend, Miyako Kagurazaka, who was also inadvertently summoned like him, being killed by one of Four Heavenly Kings from the Demon Army. Vowing revenge, Yuuto acquires the means to fight over many years and successfully defeats the Demon King including the mastermind, the goddess. However, immediately afterward, he is swallowed into the interstice of dimensions and regains consciousness in modern-day Japan before he was summoned to another world.