Sent to Earth by the war-like alien race known as the Megans, the Mega-Monsters - Rhiahn, Triax and Krollar - were sent to slay the most powerful creature on the planet, the only one strong enough to stand in the Megans' way: Godzilla.

The first of the Mega-Monsters to set foot on Earth, Triax immediately engaged Godzilla and Red Ronin, using its jets to floor Godzilla with a flying bodyslam. Soon it was joined by its brothers, Rhiahn and Krollar. Along with Krollar, Triax attacked Godzilla. Despite their superior numbers, Godzilla was able to hold his own against the two of them. With their warship crippled, the Megans made a last-ditch effort and zapped their Mega-Monsters with an Energex-Ray, doubling their size and making them all tower over Godzilla.

With Red Ronin gone and their power increased, the Mega-Monsters attacked Godzilla with all their might. But even with their enhanced strength, the three of them were no match for Godzilla's rage. Triax attacked Godzilla with a series of flying body slams, but the Monster King soon grew wise to the tactic and fired an atomic blast directly down Triax's throat.

Instantly killed by the blast, the second Mega-Monster fell from the sky, leaving its brother Rhian alone against Godzilla's might.