Yūgure is an android who mirrors the appearance of Towasa Ōmaki, a human woman from the past. She appears before Akira Himegami shortly after he awakens from a 200-year cryogenic sleep into a world transformed. Upon their first meeting, Yūgure immediately and directly proposes marriage to him, leaving Akira confused.

Despite his initial bafflement and his belief that his past love, Towasa, is still alive, Yūgure accompanies Akira on his journey to find her. Her presence and proposal lead them into an exploration of relationships between humans and androids.

They travel through a society where traditional structures have been reshaped. A new system known as "Elsie" or "LC" has replaced the former concept of marriage. Their journey examines the forms love may take, including that between a human and a robot, and questions the endurance of such a bond when one may far outlive the other.