Some 400,000,000 years after an advanced human civilization was destroyed by an alliance of planetary conquerers known as Warp Monarch, 12 direct descendants of the civilization's warriors (called Sazers) awaken their powers and join forces with the other members of one their ancestors' four tribes: Flame, Wind, Earth and Water. Each Sazer is based on a Zodiac sign represented in an animal totem or spirit representation. At first, they wage war on each other, but after learning the truth of their ancestry and their reason for awakening, the GranSazer tribes unite to protect Earth from the Warp Monarch from once again extinguishing all life on the planet.
The Wind Tribe warriors try to convince Tenma to fight for them by force, while moving forth to gaining a final member to activate their ChouSeiShin
Needing a third member to activate their ChouSeiShin, Tenma decides to search for their partner, unknowing that the Flame Tribe's final member has been there all along.
Tenma is suddenly attacked by a new GranSazer from a third tribe who is trying to find his own alliance, making him susceptible to the Wind Tribe's manipulations.
Both the Flame and Wind Tribes try to reach out to the two remaining awakening members of the Earth Tribe: a girl associated with a criminal and the officer trying to bring him in!
While trying to deal with proving the innocence of Ran's partner from his enemies, the GranSazer of the Flame and Earth Tribe try to awaken the third ChouSeiShin while the Wind Tribe continues their assault!
When a co-worker of Tenma becomes hurt by Karin, he must work to save her life even knowing that his rival Dentsuin is the doctor performing her surgery!
Professor Horiguchi researches Karin in hopes of figuring out who she is, while Ryoko confronts Mika and Ran to test if their word is actually true.
With her alliance with Karin cast in doubt, Ryoko questions the true purpose of the Wind Tribe as they come under attack from outside and within.
With Ryoko and Jin defecting to the side of the allied GranSazer, Karin continues to manipulate Akira into helping her and to eliminate any obstacles that stand in her way.
When Naoto, the only GranSazer still working on his own, is attacked by the rampaging Akelon, Kamiya and Ran must try to convince him to join with them so that the nine GranSazer could finally fight together as one group.
Both Naoto and Akira must work through their trials and difficulties in order for the GranSazer to finally unite as one and face down the Akelon invader in a final showdown!
A meteor from space reveals a new invasive force while unveiling the fourth ChouSeiShin, which comes under protection even as a famed photographer does suspicious investigations of it and the GranSazer!
Lucia continues to threaten the GranSazer in hopes of taking down Leviathan, while Radia decides to target the remaining Water Tribe members in order to deal with them to prevent its awakening.
As Tappei works with Ryouko to activate his GranSazer power, the Water Tribe try to protect their dormant Leviathan from both the military and a vengeful Radia.
Finding out about the damages that the invaders to Earth are doing to the populace, Gou tries to figure a way to stop the battles with the Impactors as Commander Logia begins to make his move.
A scientist kidnapped by Logia uses a promise to Ai to try and escape custody from activating an ancient robot the Impactors hope to use to annihilate humanity.
Ai must continue to protect Professor Wakuji from the Impactors after they discover he had pulled a trick in preventing them from fully activating Guntras.
With two ChouSeiShin defeated by Guntras, Ran takes it upon herself to convince Naoto to join in summoning Guncaesar in an attempt to stop the machine, with Ryoko likewise showing concern towards his return.
Ai and the Water Tribe try to lure out Lucia in a plot to bring out Logia and retake the Guntroller during a small opening before their final planetary destruction plan can begin.
With eight hours before Guntoras collides with the sun and destroys the solar system, the GranSazer scramble to figure a means to get the Guntroller back from Logia!
Lucia goes against Logia's orders and decides to utilize a final option in dealing with the GranSazer, making her appear unstoppable until the ultimate secret of Guntras is revealed...
Ran discovers more information about the ancient civilization as Logia begins attacking the tribe leaders in preparation for his final battle with Tenma.
The final showdown of Logia's Dailogian and Tenma's Garuda occurs, where the true extent of the Impactor's desires for revenge is revealed.
The GranSazer recollect on their battles with the Cosmic Alliance up to now as Professor Horiguchi finds himself as an unlikely target by another scientist.
The GranSazer must stop the latest plan by the Cosmic Alliance when people are suddenly sent to another dimension, including Tenma and Mika!
As the other GranSazer try to figure out how to stop the Vizar's plot of transporting Tokyo to another dimension, Ken becomes caught in a trap due to the mysterious girl Asami.
Tenma comes to the aid of a female scientist on the run for a cloned version of one of the GranSazer's defeated enemies!
With the Clone-Akelon running amuck, the JSDF and GranSazer must bring it under control before it can utilize the full extent of its massive power.
When a friend of Ryoko's appears to come back after a horrifying plane crash, she ultimately must help him dispose of an artifact that could potentially destroy the Earth.
Gou becomes the guardian for a genius girl trying to get away from her duties for the day while she's being pursued by an alien threat.
Tenma tries to protect the daughter of an astronaut when he become possessed by the spirit of a warrior from the ancient war between Earth and the space alliance!
Logia returns with a plot to stop DaiSazer while having his ultimate revenge on Tenma for his previous defeat.
Logia goes forth with his master plan of stopping the GranSazer, targeting unusual elements in order to complete his victory as Tenma tries to refocus his Impactor rival on him!
After being killed, an alien police officer takes over Jin's co-worker in order to complete its final mission.
Tappei must protect the aquatic park he works for when a Wolfmanafu warrior possesses his dolphins in a scheme to conquer the planet.
An ancient robot from the Earth/alien alliance war is activated, where it bonds with Mika while its true purpose is slowly unraveled.
The Gransazer discover the horrifying truth about the ancient android left on Earth, as Mika continues to try and prove that Omega doesn't have to follow the orders left for him in the past.
Logia returns to Earth again under the orders of a mysterious master, where he abducts Mika and Horiguchi under orders while trying to get another showdown with Tenma!
With Belzeus in full control of Dailogian, Logia contemplates his true purpose as Tenma rushes forth to have his final showdown with the Impactor invader.
The Wolfmanafu alliance sends a herald to release an ancient lifeform that appears to have a connection to the GranSazer themselves!
As the Wind Tribe try to hold off the force of the Bosquito, Tenma tries to discover more about the Wolfmanafu representative and the mystery of why the ancient creature was released.
As another Bosquito emerges after the death of the original, Professor Horiguchi and Ran make a shocking discovery about the ancient war and the truth about the connections between Earth, the ancient monster, and the galactic alliance Wolfmanafu!
The truth about Gransazer and their connection to the Bosquito is revealed as the warriors fight to defeat the unstoppable ancient monster once and for all.
As the Wolfmanafu alliance begins their final advances towards Earth, an emissary arrives to try and draw forth peace at the cost of a GranSazer's life.
Ran continues to weigh on the need for her sacrifice to stop the final Wolfmanafu invasion as the other Gransazer try to convince her to not fall into their trap.
While the Gransazer desperately try to deal with the latest giant sent by the Wolfmanafu, they likewise try to decipher the truth regarding Earth's relations to the galactic alliance and a peaceful way to possibly end the war.
As the Gransazer try to figure out what to do in regards to stopping the Wolfmanafu attack, Belzeus sends down an assassin to eliminate Ruby before she reveals key information.
With time running out before the arrival of the Wolfmanafu fleet, Tenma attempts a risky option of trying to contact their leader as Belzeus sends down an unstoppable monster to finish the GranSazer completely.
As Belzeus and Cabyron continue their assault on Earth with the alliance preparing to strike, the Gransazer must make a final stand as Tenma and Ran attempt to finally break through and bring peace between Earth and the Wolfmanafu alliance.