In a futuristic Japan, the government enforces a matchmaking program called 'The Red Threads of Science' to combat declining birth rates. At 16, Yukari Nejima, an average teen, faces a predetermined marriage partner assigned through this system. Despite this, his love for classmate Misaki Takasaki leads him to defy the rules and declare his affections. Surprisingly, Misaki returns his feelings, but their budding romance is interrupted by Yukari's government-mandated marriage notice. Caught in a tangle of emotions and secrets, Yukari finds himself entangled with his assigned partner, Ririna Sanada, who becomes intrigued by his forbidden love affair.