While searching for his missing sister, Eiji Shigure secretly enters the castle of millionaire Klein Sandman. There he meets the castles strange inhabitants and is selected to join in Sandmans mission to stop a destructive alien known as the Zeravire. The teams weapon, a series of fighting robots designed by Sandman called the Gran Kaiser and the Gran Divas who when needed join together to form Gravion.

The newly formed Gravion faces off in their first battle against the Zeravire and the pilots discover their weaknesses. Meanwhile The Earth Federation Alliance plan their own attacks on the Zeravire.

Eiji begins to get used to life in Sandman's castle and to the castles inhabitants. As he and Toga venture to the forbidden area of the castle in search of Eiji's sister Ayaka and the identity of the G-Shadow's pilot, Raven attempts to convince the EFA to allow Earthgertz to take the lead in the defense against the Zeravire.

When a ghostly figure is sighted in one of the castle's towers, Toga and Eiji go to investigate. There they discover Leele, the mysterious pilot of the G-Shadow.

In an effort to get to know each other better, the team goes on a picnic together but Leele is hesitant to share as she is haunted by nightmares of her past. Meanwhile the EFA attempts to find information of Sandman.

Eiji sneaks out of the castle during the staffs shopping day and takes Toga along with him for his first day out of the castle and his first day in the big city. As the maids search for them, the Zeravire launch an attack on the city.

On the anniversary of her father Isanas death, Luna returns home to the island of Okiaowa but is surpirsed when she finds that the rest of of the Gran Knights have decided to accompany her to the have some fun on the island. But all fun is soon ended when the Zeravire target the International Peace Conference for their next attack.

When the Zeravire attacks the the castle, all hope of stopping it lies with Eiji, who has accidentally found himself piloting the Gran Kaiser. To survive he must call upon all the power of the Gran Kaiser and all that his body can withstand.

Repairs begin on the castle following the attack by the Zeravire and Eiji begins to recover from his battle but runs from his physical and runs into Mizuki who gives him insight to the disappearance of his sister Ayaka. Together they decide to investigate where she vanished, the West Tower.

Following recent events, Sandman reluctantly has an auto-pilot device, The Gran Phantom intstalled into the Gran Kaiser in case of emergency. And one does arise when a Zeravire with a nuclear power supply attacks and one of the maids is put in danger, causing Eiji to try and rescue her while the rest of the Gran Knights use the system and go into battle with out him.

After seeing what darkness Toga is capable of in the heat of battle, Eiji quits the Gran Knights and leaves the castle to return to a normal life. Leele ventures to town to convince Eiji to come back. Two pilots down, Gravion must operate with its auto-pilot taking up the slack when the Zeravire attack.

The battle wages on as Gravion fights against the attacking Zeravire with a failing auto-pilot and Eiji and Leele still missing. But after his friend Yumi is injured in the attack, Eiji decides that his place is with the rest of the Gran Knights on Gravion.

The Zeravire have been evolving, not in order to destroy humans, but to ensure the destruction of Gravion. When the new and improved Zeravire comes to Earth to challenge Gravion, Sandman is hesitant to let the Gran Knights go to battle but they refuse to sit on the sidelines. With no other choice, Sandman must authorize the use of Gravions most adavanced weapon.

The Gravion team completes another mission, mucht to the delight of the president. Someone says the Zerevie are going to return at any moment. The team is made to be maids, due to a strip mah jongg game that got out of control. They are forced to cook, clean, do the laundry, repair robots, and more. Eiji is forced to wear a dress. Meanwhile, Mr. Sandman is meeting with someone elsewhere. Back at the mansion, Luna shows off Toga's room when he was a child to Eiji. Then the G-alert sounds. The Grand Knights go to intercept the intruder. After much destruction, they decide to combine, but cannot. He's stuck in a subway. After trashing a street punk, Sandman shows up and lets them combine into Gravion. A lot of chaos and distruction ensues, ending with the Zerieve being destroyed. Elsewhere, some generic sinister people are plotting to reshape the earth...

The gang surfs the interenet and visits Gravion's web site. Every page is "under construction" except for a headquarters map, which looks like a 3-year-old drew it. The maids blame Eiji.

It's generic trip-to-the-hot-springs episode! Raven and Cookie have stayed behind though. At the springs, fanboy service comes fast and furious. Ena is a bit shy, but her towel is taken away anyway. Eiji relaxes in the men's bath when some of the maids enter. In escaping them, he falls over a cliff with only a section of fence to protect him. He ends up turning it into a tobogan. He crashes through the women's bath. Toga joins Eiji, thinking this is a fun game. They end up crashing at the bottom, where Toga ends up on top of G-Force's commander. After getting smacked by her, Toga spies Sandman talking to a man.

At the EFA's underwater energy base, something is attacking it. They ask Gravion to investigate. Leele goes there, and they lose contact with her. The others investigate. Eiji takes Una's place. The Zerivire attacks at this point. Toga finds Leele and rescues her, only to be confronted by some mini-Zerivire. Toga forces Leele into another room while he battles the Zerivire alone. Meanwhile, just as things were looking hopless outside, the rest of the Gravion arrives. Eiji finds Toga lying on the ground, with his head in Leele's lap. After the rescue, Gravion is formed and then attacks the Zerivire. Toga has lost his sight due to lack of oxygen. However, Leele goes to him and guides his hands. Later on, Toga recovers at the base.

The gravion gang goes to an amusement park Grand Island with some of the maids. There's a Zerivire there. Back at the base, the maids protest to Raven that they want to go to the park too. Back at the park, they can't find anything wrong initially. Leele laments that she doesn't have any memory of her past; the others tell her that she can simply make some by being with them. Leele and Toga are in a skyride by themselves, and Leele makes a move on Toga.

Elji and the others suspect that Sandman is hiding something connected to the frequent Zelabaia attacks, and they sneak into the north tower of St. Germain Castle. There they discover the Sandman's mysterious past and the secrets behind the creation Gravion. Some of the mysteries behind Leele's birth are also unveiled, and when Toga tells her about it, she is so shocked that she throws herself into the Lake.

The Earthgultz members are worried about Leele. Toga in particular is berating himself becuase he always seems to hurt the people around him through his own carelessness and inability to understand their feelings. Zelabaia attacks while Toga is still upset, and his agitation keeps Gravion from functioning properly, making it flounder in battle.

Sandman is keeping vigil on his daughter when the news comes: Toga's gone missing. Hugi has been watching this all this time, and gloats over this. It's going his way now. Eiji goes out after him.

Leele finally awakens from her coma. Eiji's out looking for Toga. Faye takes Toga to the orphanage where they grew up. It was sponsored by Sandman. She tells him that she resents him for taking her position as the Gravion's pilot. Faye tries to recruit Toga into the Grand Troopers. Just as he's about to give into her, Eiji arrives.

There's a new Gravion called sol Gravion. Zieg recognizes its power source as a device that decimated an alien race. It turns out the main pilot of the Sol Gravion is Ena. Ena tells us she's a clone of the original that died, but has all the memories of the original. The Zerivire apparently leave (yet another unexplained plot hole.) The Gravion team takes the Sol Gravion for a test spin. Sandman tells us that the Sol Gravion has the power to destroy the world - or create a new one. Eiji and Toga make up for their fight. Sandman frees Eiji, saying he has no obligations to Sandman anymore.

The Gran Knights and the rest of the castle take to space in order to take the battle to the Zeravire homeworld. It is the beginning of the final battle, where the fate of the universe will be decided.

This is it, The final battle for the fate of the universe has begun as the Gran Knights and Sandman take on Hugi and the ulitmate Zeravire weapon. As the whole world looks on, our heroes must band together like never before to ensure the saftey of mankind. Win or lose, it is time for the end and time for goodbyes.