Beast King GoLion (1981)

In the year 1999, five space explorers return to Earth after their latest mission. They find out that the human civilization was wiped out by World War III during their absence. The explorers are captured by the Galra Empire, but they managed to escape and make their way to the planet Altea. Princess Fala, the 16-year-old ruler of the planet, recruits them as the new pilots for the long-dormant robot GoLion. The princess and her pilots have to defend the planet from the empire.