After a mysterious magical event whisks him and his peers to the fantastical world of Tortus, Hajime Nagumo, labeled as a 'Synergist' with unimpressive combat abilities, faces ridicule from his classmates. When a dungeon expedition turns perilous, Hajime sacrifices himself to save the group but gets flung into the dungeon's depths. Determined to survive and ascend to the surface, he embarks on a harrowing journey of self-preservation.