Yui Mitsuya and Masugu Tateishi work at Tsuda Confectionery, a sweets manufacturing company, and they are notorious office enemies. Their frequent, fiery clashes in front of their coworkers have earned them the nickname the mortal enemies. Yui works in the planning department while Masugu is in accounting, and both joined the company at the same time.

Contrary to their public personas, they are deeply attracted to each other and eventually begin a romantic relationship. Worried about workplace gossip and the complications that can arise from an office romance, they agree to keep their new relationship a secret. This forces them to maintain their carefully crafted façade of mutual dislike during work hours while navigating their hidden love outside the office.

Masugu is a diligent and meticulous accountant with a humble and kind-hearted nature that makes Yui swoon. He is originally from Yamanashi Prefecture, where his family runs a grape farm. Yui, who initially found Masugu too stiff and boring, eventually falls for his genuine and caring personality. She is later transferred from the planning department to the public relations section, a change that further impacts their dynamic.

The narrative follows their daily struggle to keep their hands off each other and their relationship concealed, all while risking exposure with every interaction at the office. Key arcs include Yui adjusting to her new role in public relations and the challenges left behind in her old department, including a friend facing a family crisis that leads to a breakdown. The story also introduces potential romantic rivals, such as a tipsy colleague who makes her adoration for Masugu obvious and confronts Yui. After navigating these workplace and relationship challenges, the two eventually marry and have a daughter named Tsumugi.