Heroic Purgatory (1970)

Rikiya Shoda is an engineer working for the Atomic Agency in Japan after spending a few years studying at the MIT. He's working on a new project involving the creation of laser beams. One day, his wife Nanako, comes back home with a lost teenager called Ayu. A man, who pretends to be Ayu's father, come to get her back but Ayu keeps telling him that Rikiya and Nanako are her parents. With this girl entering their peaceful life, Rikiya suddenly begins to remember his youth, when he was a revolutionary.