Two Japanese office workers, both named Fujisawa Katsuya but with different given names represented by distinct kanji, find their fates intertwined after a violent confrontation on a rainy night. The first, a 26-year-old playboy and heir to the founder of a major company, is arrogant, sexually aggressive, and uses his position to pursue women. The second, a timid 35-year-old, is passive, easily pressured, and lives in fear of losing his job. After an altercation in which the younger Katsuya attempts to assault a female coworker, the older Katsuya intervenes, and both men are knocked from a bridge into a river below.

When the timid Katsuya regains consciousness, he discovers he is inhabiting the handsome, athletic body of the younger, wealthier Katsuya. Dazed and confused, he uses a smartphone to find his way to a luxurious condominium, where he is greeted by Reiko, a beautiful woman who claims to be his wife. Reiko is the daughter of a family who owns a winery, and her marriage to the younger Katsuya was an arranged business transaction meant to facilitate an acquisition. Despite being married for half a year, the couple has never been intimate, as her husband preferred the company of hostesses and other women.

Struggling to maintain his cover, the timid Katsuya cannot reveal the body swap to Reiko without sounding insane. When she initiates a sexual encounter, believing he is finally showing her attention, he reluctantly participates, beginning a strange and physically intimate relationship with a woman who is technically a stranger. He makes a private vow to eventually find a way to return her real husband to her, forcing the two to live together as a secret couple bound by circumstance. Meanwhile, the young playboy’s body is missing, and police assume he has drowned.

The timid Katsuya also faces challenges at his workplace, a beverage subsidiary called Takaraou Drink. His new body belongs to a notorious womanizer, so female coworkers greet him with suspicion, and Momoko Asagami, the kind junior employee he secretly admired before the swap, openly slaps him and expresses her relief that her crush, the timid Katsuya, seemingly died in the accident. Unable to reveal his true identity, he endures her hatred until he privately recounts a memory only the real timid Katsuya could know, slowly convincing Momoko of the truth. She becomes his only confidante.

As Katsuya adapts to his new life, he discovers that inhabiting a more confident and handsome body grants him a charisma and assertiveness he never possessed before. He excels at a business presentation and is partnered with Momoko to pitch products to a luxury retail chain. Their negotiation takes them to the eccentric president, Onizaki, a blonde woman who conducts business meetings in her office bar through drinking games and sexual challenges. Katsuya is forced to navigate these encounters while maintaining the false reputation of a playboy, all while secretly being an inexperienced virgin.

A notable arc involves a visit to Reikos parents at their countryside winery. Here, the true nature of her cold, transactional marriage is exposed. Reikos family arranged the union for financial gain, and she had resigned herself to a loveless life. After this trip, Katsuya formally declares to Reiko that he will pretend to be her husband and protect her until the day her real husband returns and they can swap back, solidifying their partnership as a secret couple. The story follows their increasingly complicated domestic life, Katsuya’s double life at work where he is hated for being a scoundrel and admired for his sudden competence, and the ongoing search for the missing original body, all while exploring the sexually charged and often absurd situations that arise from this mistaken identity.