A female office worker, still pining after a senior colleague she often stays late with, stumbles into the break room one evening and witnesses that same man having sex with another woman during overtime. Shocked and unable to move, she is pulled away by Araki, a blunt and teasing coworker in her own cohort. When she laments that she never had any such development with the senior despite all their shared late nights, Araki pushes her to the floor and points out that if he were to sleep with her right now, it would count as overtime sex too. The story unfolds in a Japanese office setting where late-night work is common, and the title's premise holds that a large portion of coworker overtime encounters escalate into physical intimacy. The female lead, a spirited but romantically uncertain employee, finds herself caught between her lingering feelings for the senior she admired and Araki's persistent, offhand advances that begin to feel less like jokes. As she navigates her heartbreak and confusion, a new, more aggressive male coworker enters the picture, further complicating her emotional landscape. The narrative follows her slow, chemistry-driven reawakening, with Araki's snarky demeanor hiding a genuine interest, and explores the shifting dynamics among the small office group. The story develops through a series of workplace interactions, after-hours encounters, and moments of jealousy and realization, portraying an adult romantic entanglement where personal and professional boundaries blur.