On Christmas Eve, three homeless people living on the streets of Tokyo discover a newborn baby among the trash and set out to find its parents.

A giant sea monster known as Dragonsaurus has emerged from out of nowhere, terrorizing the depths of the oceans. Great Mazinger, Grendizer and the Getter Robo G team join forces…

Alien invaders take over Great Mazinger who is at the entrance of a museum next to Mazinger Z as symbols of peace. Grendizer fights the evil invaders and Great Mazinger…