Japan, 1944. Trained for intelligence work, Hiroo Onoda, 22 years old, discovers a philosophy contrary to the official line: no suicide; stay alive whatever happens; the mission is more important than anything else. Sent to Lubang, a small island in the Philippines where the Americans are about to land, this role will be to wage a guerrilla war until the return of the Japanese troops. The Empire will surrender soon after; Onoda, 10,000 days later.

Mizuki's husband (Yusuke) drowned at sea three years ago. When he suddenly comes back home, she is not that surprised. Instead, Mizuki is wondering what took him so long. She agrees to let Yusuke take her on a journey.