In a futuristic society, Japan has established a complex system known as "The Red Threads of Science" to promote successful marriages and address declining birthrates. Based on compatibility calculations, the government assigns marriage partners to young people at age 16, with severe consequences for those who defy the arrangement. For Yukari Nejima, a teenager who views himself as average in every respect, this system may represent his best chance at a fulfilling life. However, driven by his infatuation with his classmate and long-time crush, Misaki Takasaki, Yukari defies the system and confesses his love. After some initial hesitation, Misaki reciprocates his feelings in a moment of passion. Unfortunately, before the pair can deepen their relationship, Yukari receives his marriage notice. He is then drawn into a confusing web of love and lies when his unenthusiastic assigned partner, Ririna Sanada, becomes fascinated with his illicit romance.