Super Robot Retsuden is a crossover manga series featuring all of the major mecha series by Dynamic Productions: Mazinger Z, Great Mazinger, Getter Robo, Getter Robo G, Steel Jeeg, and Grendizer. Most of the artwork was done by Ken Ishikawa and his assistants, hence why the Getter Robo robots have the most screen time.
Summary[]
An alien threat known as Varon threatens Earth by sending down Meteor Beasts to attack the planet. The mechs from Japan's multiple institutes fight against them while giving a helping hand to one another when they are in dire situations. By the time the fight goes into space, the Grendizer appears to even the odds. Despite both Varon and Jeeg's apparent destruction, strange events continue to occur. Varon and Jeeg have revealed to have both survived with Hiroshi Shiba giving crucial information that Varon is recovering. The Getter Robo is badly damaged but is replaced with the Getter Robo G including a new pilot Benkei Kuruma to fill in for the injured Musashi Tomoe. The five robots take the battle to the moon for a final showdown with Varon using a special convoy that transforms into the Hyper Robo Dynamic Saga and after a lengthy fight, deliver the final blow to Varon with the heroic robots ready for whatever else the universe will throw at them.