Hajime Nagumo, an unremarkable high schooler summoned to a fantasy world alongside his class, receives the weakest job — Synergist, a crafting skill — while his classmates gain combat powers. During an expedition into the Great Orcus Labyrinth, a classmate's betrayal sends him to the abyss below, where he loses his left arm and survives by consuming monster flesh that reshapes his body. Armed with weapons he forges from scratch, Hajime frees Yue, a vampire princess sealed in the labyrinth for three centuries.