After a bus accident claims his life, the workaholic Atobe Arihito wakes up in a realm of reincarnation known as the Labyrinth Country. To his surprise, he encounters his former manager, Igarashi Kyouka, who enlightens him on their new roles in this world. Here, reincarnators must select occupations and assemble groups to battle monsters within Labyrinths. Despite Kyouka's expectation for them to reunite, Arihito resists due to his familiarity with her strict demeanor. As they part ways, Kyouka swears to make him rue his decision. Thus commences Arihito's journey as a 'Rearguard.'