It is the year 2041 AD. An unknown object from the enemy suddenly appears in the solar sytem. An enemy named Zerabaia. Destroying the base of every planet it crosses, the vicious weapon draws closer and closer to Earth. But, this invasion of Earth was already known...
Secretly preparing for battle, a man named Kurain Sandoman commands the the army Aasu Garutsu to fight back. And their trump card is the "Gravion". A human shaped Mecha that was made to unite with with other huge units named GD.
That day, when Zerabaia began its attack on Earth, a young man was looking for his sister who's disappeared. Off to look for clues, he sneaks into Sandoman's base. It was there, in the hangar, that he met another mysterious young man.
"You're the same as me... I knew you were here... Another boy like me".
He gives a smile that seemed to show he doesn't have a care in the world. He was main pilot of "God Gravion", Touga. The GD that Eiji dreamt of escaping in in a dream.
Eiji was suddenly registered automatically as a pilot and was forced to go out into battle. Trampling through the towns, the huge weapon shaped like a sword, Zerabaia, appears in front of Eiji's GD. And so Touga's Grankaiza-, Luna, Eina, Mijiki and a mysterious girl rushes to its place.
Eiji doesn't even know what he's doing in the cockpit. And so, the 5 Mechas join and form "God Gravion"! The Earth's fate is now in these 5 young people's hands!