Ten years after his isekai adventure ended in triumph, the former hero Yuta Shimabara finds himself trapped in a mundane and stifling daily life. Once a salaryman who was struck by a truck and reincarnated into a fantasy world, Yuta used his overwhelming power to defeat the Demon King, rescue a captive princess, and become the realm's greatest hero. He married that princess and settled into a life of comfort and status. But a decade later, his marriage has become sexless and emotionally distant. The princess, his wife, sees no need for physical intimacy after producing an heir, leaving Yuta restless and unfulfilled.

Seeking an escape from the tedium, Yuta reconnects with Luca, a female warrior who was once a member of his original Demon King subjugation party. Luca has since lost her husband, leaving her widowed and also yearning for connection. Their old bond quickly reignites, and the two fall into a passionate, forbidden affair. As the relationship deepens, Yuta is promoted to the position of new king, and Luca is appointed as the new Minister of Military Affairs, giving them even more proximity and opportunity to continue their secret relationship. However, their clandestine meetings draw the suspicion of those around them, including the finance minister, Marcute, who eventually discovers the truth.

The story follows Yuta and Luca as they navigate the thrill and danger of their illicit romance. They embark on a secret trip together, revisiting the locations of their adventures from a decade earlier, rekindling both their past memories and their physical passion. As the affair intensifies, the risk of exposure grows, forcing Yuta to confront the consequences of his actions. The series explores the emotional and moral dilemmas of a hero who has achieved everything but still feels empty, and the destructive yet compelling pull of a love that cannot be openly acknowledged. The narrative concludes with Yuta having to make a definitive choice about his marriage, his throne, and his future with Luca.