Gau Gau was the Monster of the week in Ep.42 of the Grendizer Anime and its major role was to keep Grendizer along with M-Spazer at Bay while the Vega fleet attacked the Space Center, was more of a filler monster for the true events that took center stage in the Episode's plot, and was destroyed quite easily with one swipe of the Double Harken without much of a fight to show for. The Episode marked the introduction of the Mothership Fortress, commanded by General Gandal, and the reveal upgrades of the Space Center as a combat ready Fortress.

Gau's Saucer mode was a standard flat purple disk, with gray two curved spikes and yellow triangle markings around the shell; the Robot mode was humanoid in shape, with a red head and torso; arms were gray and red-purple with purple hands, gray and red-purple legs; it possess a red helmet with horns and a mouth plate. It had a gray abdomen, black pelvis, with horns on the side, and black shoulders. Its saucer shells where attached by support on the shoulders. It had super strength and laser eyes.

The Makiba sees a truck passing by on direction to the lab, they head to observatory and learn is a shipment of a new super computer for the facility, which is going through massive renovations in preparation for the escalating war with the Vega Forces, specially as the the enemy knows that the Center has a connection with Grendizer, with power generators been installed around the site. At the Skull Moon Base, Gandal receive word that the Energy crisis has been resolve, with a new source having been discovered, with it the invaders can bow go back to a full war footing, with a plan of attack at the Center. Taking time to make the plan, Minister Zuril begins work on the new Battleship as well.

Side note: Yes, the whole energy crisis is over after five Episodes - MAKING THE WHOLE DRAMA POINTLESS!! This is when you realize how an effective Dr. Hell as villain was when he and his henchmen succeeded in stealing Alloy Z that one time, or blowing up the old Pilder having Mazinger Z out of commission for a few episodes. I'm not lying, when I say I was really disappointed about this sudden resolution.

Back at the center, the new Computer is installed and ready to get running, but Umon finds no heart to turn the machine online; in a later conversation with Daisuke, he explains it was dream to use his Center to solve every last mystery of the universe, but did not expected it would be use as a tool or war.

Undetermined time later, Gandal launches his assault Fleet, led by the new Warship (the Mothership Fortress) and saucer Beast Gau Gau accompanying them: it deploys the fleet and beast to attack, with the Center detecting them. Koji launches first and meets the first wave, disposing of the Minifos, when the 2nd wave with Gau shows up. Duke launches and helps Koji out, but the Beast dives into a nearby lake, Hikaru then joins on M-Spazer and connects, but the two are dragged underwater by Gau Gau. With Grendizer and Marine Spazer held by Gau, Gandal and the rest of the fleet launch a full assault on the Center to destroy it; deducing their scheme, Duke warns the others and tells Umon to activate the New Computer, when he loses contact as the Warship arrives.

The Center activates the energy shield generators, but these overheat and fail immediately, with the Observation Platform descending into the Refuge Bunker. The Minifo Fleet trashes the site, with Koji shutting down a few in a desperate attempt to protect the Center, though Umon request that he doesn't risks himself and retreats, much to the protest of the former. As Gandal readies to use the Vegatron Canon for the deathblow, Umon begins to activate the Computer, while Grendizer frees from the Beast by using M-Spazers Exhaust propulsion, bashing the monster with the rock. Duke and Hikaru leave to join Koji in the center when Gandal opens fires at the it, seemingly destroying it when to the General's horror, a new dome structure emerges from the smoke and debris of the site, with the Center itself having survive: the Shuttle Dome opens, revealing Hangar platforms and Laser canons, and the new Combat Center takes on the fleet destroying the Minifos, with Grendizer blowing up the Vegatron Canon for good measure. Realizing the tide of Battle has turn, Gandal orders retreat, with Duke on his trail, though Gau Gau cover his escape. Grendizer finishes the Beast with a single swipe of the Double Harken.

After the battle, Umon explain he had rebuilt the Space Center in secret.