In the year 2050, the world teeters on the brink of a third world war. Marukun, aided by Shizuka-a sparrow with the power to manipulate time-embarks on repeated journeys through time, starting from 2025. His travels span eras of conflict, from the present day to the chaotic "Great War of Wa" in the Yayoi period. Chosen by Himiko as the inheritor of the ancient art of Kidō (spirit way), Marukun becomes a vital link between distant ages. Upon returning to the present, he brings peace and hope through technological innovation and education, reshaping the future with quiet resolve. Meanwhile, a young girl named Momoka, still in elementary school, stumbles into a parallel world. There, she confronts a malevolent demon bent on driving people to madness and war. Armed only with her pure heart and courage, Momoka joins forces with newfound companions to thwart the demon's schemes and protect the real world from its shadowy influence. As her adventure intertwines with Marukun's temporal odyssey, both play crucial roles in averting global catastrophe. In the end, Marukun and Momoka, each walking their own path, seek the essence of "what fades with time and what remains." Through their choices, growth, and the bonds they forge, the story reaches a moving conclusion that resonates deeply with the reader.