Sora tobu yûreisen (1969)

Hayato's peaceful life with his parents and his dog is brought to a dramatic, terrible end when a giant robot, said to be sent from a flying ghost ship, devastates the city, killing hundreds including Hayato's parents. Shortly before his death, Hayato's father reveals that he is not really their son. Hayato is now alone, struggling in this strange new world left after the disaster, where giant machines and monsters control the world. He sets on a dangerous quest to discover the mysterious powers that be, only to discover that he is directly connected to it all...