High school student Saiga has his daily routine disrupted when his family gets news that his Father's remains have been found after years of being missing near a triangular mountain in Japan that some believe is man made. A meteor with a strange robotic lifeform falls from the sky and begins to cause destruction. This causes a bracelet from his father's research to activate and merge him with an ancient robot buried in the pyramid whose known as Reideen who will now help save humanity.
A gigantic robot is discovered and could be the catalyst that will turn the tide of war for one ravaged nation.
The new war robot is named Reideen. Saiga has difficulties controlling it before he is thrown into the fray.
Saiga has gained a great mastery over Reideen, but everything else is clouded in shadows. Another threat appears while the Vigilance Corps deals with further disaster.
Saiga and his friend are driven underground and backed into a corner. As a new enemy threatens them below, a new alien wreaks havoc above ground.
The Vigilance Corps tries to find a way to contain Reideen, but it seems that only Saiga can control it. Meanwhile, an aerial beast presents a new set of problems.
Saiga continues to resist any type of help from the Vigilance Corps. Reideen faces a threat from the sky that it is ill equipped to handle.
The Vigilance Corps refuses to sit on its laurels while the world is in danger, debuting it's latest mechanical wonder, the Hayate. Things go from bad to worse as they lose control of their new toy.
A berserk Hayate takes flight, bringing with it a large amount of explosives. A plan is hatched to destroy it over the ocean, but it seems that there is still someone trapped inside.
A mysterious blackout rolls through Tokyo. Under cover of darkness, a new mechanical beast emerges from the bay.
This new mechanical beast surely caused the blackout, but it refuses to attack! As Saiga learns more about his foe, he'll have to find a different way to take it down.
The suburbs of Tachikuni are the staging area for a new alien offensive. But as they study the mysterious new structures, a new mechanical beast attacks from the sky!
Saiga is held prisoner on a giant alien ship. There he finds Gadion's pilot , Roxel. A battle ensues between the two, and the prize is Reideen itself.
Even though Reideen has won countless battles, there is still a lot of mystery surrounding it. The White Heron Squad travel with Saiga to Mt. Kurokami in hopes of discovering clues there.
Summer time arrives and Junki and his classmates go swimming at the beach. Little do they know, a mechanical beast is lurking, waiting for a chance to ruin the summer fun.
With the water making it difficult to for Reideen to maneuver, the mechanical beasts close in to attempt to potentially put the nail in Reideen's coffin.
Strange weather arrives without warning. Snowing in the summer and hurricanes forming over the city have signaled much worse thing to come. With no where to go because of the storm, a monster makes it's way into the school.
Junki and his classmates are attacked by Rakas, and the true purpose of the storm is revealed as a way to keep Junki separated from help.
Junki is shocked to learn that Hoshikawa is going to leave the White Heron Unit.
Intrigued by Hoshikawa's psychic ability, Junki is captured by a mechanical beast in his attempts to learn about Hoshikawa's history.
The mechanical beasts trap Reideen's attacks while the activities of the Vigilant Corps. are investigated.
Ando's actions put the White Heron Squad in danger and Junki remains unreachable. Captain Maedasaki is called in to bring order to the rifts that have been created amongst the Corps.
Junki awakes after being badly beaten while trying to rescue the princess from the demon lord Jinzen. He is accompanied by Edoleni who supposedly saved him and a cat-girl named Orichi. Junki begins to question whether this is real or if he is dreaming.
An alien who Junki knows of is coming to Earth. His target may be Reideen who must be protected at all costs.
Junki is unable to go with Reideen because his bracelet had been stolen by Roxell. Meanwhile, the extraterrestrials are launching their attack in full force and the Hayate Squadron must launch a counter attack.
The White Heron Squad and Junki take off to the giant spaceship to rescue Reideen and Gaidon.
The fight continues between Reideen and Gaidon and the extraterrestrials attack en masse. With the Fate of the Earth in the hands of Junki only time will tell if mankind will survive.