Hidden between the 4th and 5th floors in downtown Seoul — invisible to the living — lies an office where Grim Reapers manage the dead. Here, Reapers are graded on case volume and service scores — a world where even death runs on systems and KPIs. Jun-ho, a by-the-book rookie, is paired with Gang-rim, a smoothtalking veteran ace, on his first case. But whether he follows protocol or breaks it for the dead, the outcome never makes sense. Questioning this "perfect system," Jun-ho recovers memories of his past life while guiding the soul of a developer fated to die of overwork — then touches the forbidden to extend one human life, cracking the system itself! A rules-obsessed rookie x an endlessly flexible senior: the worst match becomes the best buddy duo — an office human drama about the "people" no system can explain.