In a near-future Japan, the government enforces the "Red Threads of Science" system, a program designed to combat declining birth rates by assigning marriage partners to citizens at the age of 16. Yukari Nejima, a high school student, is deeply in love with his childhood friend, Misaki Takasaki, and plans to confess his feelings before their government-assigned partners are revealed. However, before he can do so, Yukari receives his official notice: he is paired with Ririna Sanada, a calm and composed girl from a politically influential family. Despite this, Yukari confesses his love to Misaki, who reciprocates his feelings, creating a complex love triangle.

The series explores the tension between personal desires and societal obligations as Yukari, Misaki, and Ririna navigate their relationships. Misaki struggles with her feelings for Yukari while grappling with the fear of defying the system. Ririna, though initially distant, begins to develop genuine affection for Yukari, complicating the dynamic further. The narrative delves into themes of love, duty, and individuality, as the characters confront the consequences of their choices within a rigidly controlled society.

Yukari’s internal conflict drives much of the story, as he balances his love for Misaki with his growing bond with Ririna. Misaki’s determination to pursue her feelings despite societal pressure adds emotional depth, while Ririna’s evolving perspective on love and marriage provides a counterpoint to the system’s impersonal nature. The series examines the impact of the government’s intervention on personal relationships, highlighting the struggles of young people forced to reconcile their emotions with external expectations. The interplay between the characters’ emotions and the constraints of their world forms the core of the narrative, offering a poignant exploration of love in a dystopian setting.