"365 Days to the Wedding" centers on Takuya Yamada, a 28-year-old systems engineer who leads a solitary life, prioritizing work over personal relationships. His routine is disrupted when his company announces a new policy requiring employees to either marry or relocate to a remote branch. With no romantic prospects, Takuya faces the daunting task of finding a spouse within a year to avoid an unwanted transfer.

Enter Rika Sonezaki, a pragmatic and career-driven colleague who shares Takuya's predicament. The two strike a deal to enter into a marriage of convenience, agreeing to marry each other to fulfill the company's requirement while maintaining a platonic relationship. Their arrangement begins as a purely transactional agreement, but as they navigate the complexities of their fake engagement, their interactions grow more nuanced and emotionally layered.

The narrative explores the evolving dynamics between Takuya and Rika as they confront societal expectations, workplace pressures, and their own insecurities. Takuya, initially awkward and reserved, gradually opens up as he learns to balance his professional and personal life. Rika, who initially views the arrangement as a practical solution, begins to question her own feelings and priorities. The story delves into themes of companionship, self-discovery, and the blurred lines between convenience and genuine connection.

Supporting characters, such as their coworkers and acquaintances, add depth to the narrative, providing both comedic relief and moments of introspection. The series balances lighthearted humor with poignant moments, capturing the challenges and uncertainties of modern relationships. Through its exploration of love, commitment, and personal growth, "365 Days to the Wedding" offers a thoughtful portrayal of two individuals navigating an unconventional path toward understanding themselves and each other.