The story revolves around Duke Fleed who is a survivor of the Vega Star, raised by Dr. Umon as his adoptive son, and known as Daisuke Umon on Earth. Years after his arrival, he's faced with the threat of King Vega and his army, who want to conquer the Earth. With his friends Koji and Hikaru (and later his kid sister Maria Grace), Duke decides to fight back using his best weapon, the almighty Grendizer.
Episode 1
Koji Kaboto tries his OVT that he made with pieces of mecano. When flying, he is attacked by the UFOs of Vega. Fortunately Duke Fleed arrives on time to save the day (but not too quickly nonetheless). Koji does not actually know that Duke Fleed is the prince of Fleed.
Episode 2
Koji discovers the identity of the Duke Fleed, but has no time to ask questions because Vega attacks. Duke Fleed and Koji unite their power and push back the enemy.
Episode 3
Dampee Makeeba organizes a party at the ranch and invites Koji and Duke Fleed. The latter has no time to eat anything because Vega attacks. Will he have the time to make it to Grendizer before the earth is ravaged? All bets are open...
Episode 4
Gandal wants to discover the hiding place of Grendizer. So he launches a massive attack. Koji tries to confront the enemies alone, but he only succeeds to crush himself on a deserted island. Finally Duke Fleed makes it there and saves the day.
Episode 5
Koji, Hikaro, Goro and Bunta are taken in hostage. Actarus interrupts his siesta to free them.
Episode 6
Hikaro leaves for Perlepolis with Bunta. Their bus is attacked by a monster of Vega. Koji distracts the monster the time that Duke Fleed arrives (Grendizer has trouble to start up in winter).
Episode 7
Janus, from the fearsome Ruins' Division, attacks Grendizer that is powerless in front of the brutality and the agility of his enemy.
Episode 8
Blaki sets a trap to Grendizer by hiding mines in a cloud of spatial dust. Koji falls in the trap. Fortunately Duke Fleed helps him and destroys the Golgoth 8.
Episode 9
Koji is captured with his UFO by the Vegans. Grendizer attacks the camp of the black Moon to save him.
Episode 10
An inhabitant of the planet Rubi is contacted by Vega to explode the UFO carrier of Grendizer. The mission fails because of Duke Fleed and the Vegans try to kill the Rubinian. But Duke Fleed flies to his help.
Episode 11
The Vegans plan is to bring Grendizer to the shadow of the moon during the eclipse because Grendizer's systems will shut down temporarily under it and then destroy it.
Episode 12
Daisuke and Kogi are sent to investigate an avalanche and to find survivors. They find a girl named Mirana who lost her memory. Back at Space Science Centre she begins to remember how a saucer destroyed her home.
Episode 13
A new Vegan mecha comes to destroy Earth. It sucks power from the sun and burns everything in its path. Grendizer is damaged by it and has to withdraw. As the mecha attacks again Grendizer has to go to battle weaponless.
Episode 14
Boss, Nuké, and Mocha are in this episode. They are visiting their old friend Koji Kabuto. The Vegans keep their eye on a mysterious orange robot that is found skiing near-by. Commander Blacki orders the Minifo to follow it and investigate.
Episode 15
Commander Yara is forced to create a mecha that creates earthquakes and use it on the city Kanto.
Episode 16
A Vegan pilot lands near the Space Science Centre and makes Mr. Hayashi's fiancé, Kaori, a spy for him. She takes Dr. Umon as a hostage.
Episode 17
The Vegans begin building a base for their operations on Earth. The saucer "Giba Giba" begins to attack but Grendizer comes to save the day by saving a town and a mountain.
Episode 18
Dr. Umon made a project so that Grendizer is able to launch without revealing his whereabouts to the enemy. Kabuto is control by the Vegans and fights Duke.
Episode 19
A huge meteor is headed straight gives order to fire on the meteor and change its course to head for the planet Earth. The meteors are detected and Grendizer launches to intercept them before they hit land.
Episode 20
Daisuke gets the suspicion that the Vegans may be planning to pull the moon down to Earth. Duke Freed launches Grendizer and follows Koji who already went to explore the area of Mount Kirofoki.
Episode 21
The Vegans plan to melt ice in the North Pole. This will cause the sea level to rise with catastrophic results to the shores on Earth.
Episode 22
The Vegans are planning to steal Dr. Chibana's new device so that they can use it to silence Duke Freed and his Grendizer.
Episode 23
The Vegans continue their attempts to discover Grendizer's secret hideout as they are sure that the Space Science Centre has something to do with it. Hikaru finds out who Daisuke really is.
Episode 24
Commander Witer successfully sneaks into Earth as Dr. Space who is a well-known acquaintance of Dr. Umon and a reliable person so he can find Duke Fleed and kill him.
Episode 25
uke Freed's childhood friends Nayda, brainwashed by the Vegans, attempts to put a bomb on Grendizer but Duke stops her. Nayda accuses Duke of being a traitor. Koji attempts to pilot Grendizer but is almost killed.
Episode 26
Dr. Umon sends Koji and Hayashi on a mission in outer space to build a satellite station. At the same time, the Space Science Centre is surrounded by a huge Minifo saucer squadron.
Episode 27
Grendizer's delicate weapon systems malfunction and he finds himself struggling against the enemy. The Vegans arrive and descend upon the Center. Hikaru and Daisuke must fix Grendizer and save the Center.
Episode 28
General Zuril is a brilliant scientist who will try to find different ways of taking down Grendizer. Daisuke, Hikaru, and Goro are attacked by Vegans and Danbi puts on his gear and begins fighting them too.
Episode 29
Vegans shrink the cells of the living body to make Harook become a young boy for a time so he can spy Space Science Centre. Harrok and Goro become friends but later the effects of the shrinking begin to wear off so Harook captures Goro.
Episode 30
A strange rock full of radiation energy lands on Earth and Dr. Umon can't make much of this new phenomenon. At the same time, the Vegans discover this strong source of energy and put it to use in their next saucer beast.
Episode 31
The Boss, Koji, and Bunta go to the Boss Borot to begin their counterattack of the Vegan attack on them but will face some technical difficulties. Grendizer gets into some trouble while trying to help them but the Boss Borot will help Grendizer in the funniest way but will lose his Boss Spazer.
Episode 32
The Vegans send a woman by the name of Marian who looks identical to Duke Freed's mother who passed away on planet Freed.
Episode 33
The Vegans send a bird named "Zari Zari" to distroy Grendizer, but Duke remember a similar bird from his home planet Fleed and will use this knowledge to go and finish it off.
Episode 34
Vega promised Commander Gos that if he kills Duke Freed then Vega would spare the Wolf Planet from Vegan brutality.
Episode 35
General Gandal assigns Commander Beetle with his saucer beast to attack the Space Science Centre from underground. Meanwhile, Koji Kabuto's new Double Spazer ship has just been completed and Koji is ready to be air-born again.
Episode 36
Dr. Umon calls Daisuke and Koji to show them the way that Grendizer and Double Spazer can unite together and fly. The objective of this is to minimize the need for Grendizer to have to lock in and out of Spazer as these are Grendizer's weakest moments and he is helpless in them.
Episode 37
The Vegan plan is to steal a huge capsule full of Super Uranium from Earth. Vegan forces are dispatched immediately to do just that.
Episode 38
Hikaru becomes a pilot. Duke Freed faces another Vegan saucer beast loaded with Vegatron rays, and Koji nearly gets captured by the Minifo after gathering the energy but manages to escape very injured.
Episode 39
Danbi tells Daisuke that his daughter is outstanding and capable of helping him and Koji. Daisuke disagrees insisting that war and sport are two different things. Finally Daisuke will allow Hikaru to be part of the team after her vital help.
Episode 40
A series of explosions start to occur under the sea and General Zuril wastes no time in discovering that this is raw Uranium. Saucer beast "Boi Boi" is launched to go and get this energy as this saucer beast naturally collects Uranium. At the same time Dr. Umon is alerted by these explosions which are close to an island with a Uranium capsule.
Episode 41
Hikaru loses her consciousness during training and Duke Freed gets injured and his old wound gets worse. The Vegans begin their attack and Daisuke goes to the battle even though he is injured.
Episode 42
Dr. Umon's Space Science Centre is undergoing some major changes to keep up with Vega's attacks. A super computer is installed in the base, and turning it on will be the final step. The Vegans plan to get rid of the base and leave Grendizer without a place to hide.
Episode 43
A strange meteor heads slowly towards Earth and Koji will go unilaterally and see what it's all about. After nearly getting blinded by a ray that came out of the meteor, Koji's Double Spazer begins to exit the Earth's atmosphere.
Episode 44
A young man by the name of Hiyoshi is very interested in searching for ancient evidence to prove that spacemen came to Earth in the past. He goes to look at walls in a near-by cave for ancient scripts to prove his theory, but the villagers think he is crazy. Hundreds of years ago, the Vegans had sent some of their people to Earth. There still is a metal on the wall that they used for landing, and this metal cannot be detected by the radar.
Episode 45
With his telescope, Goro spots a meteor that splits in two with each piece landing in a different mountain. These actually contain eggs of the Vegan ants. When Goro tells everyone about it he is not taken seriously. Soon Grendizer and Drill Spazer will unite to face the new danger.
Episode 46
Vegan robot sharks land one night and are hidden in a public pool for their next plan. Koji finds himself a hostage of the Vegans who tell him about their plans to take all of the people as hostages.
Episode 47
Danbi induces a race between Daisuke and Koji. Koji takes it to seriously. The group goes camping near a lake. Vegans begin to descent in the lake and then the Space Science Centre suddenly gets attacked by missiles from the near-by lake where the Vegans stay hidden.
Episode 48
Duke Freed unites with Koji and the Drill Spazer to chase a Vegan saucer beast. The Vegans make an acid swamp to sink the Space Science Centre.
Episode 49
Maria tries to kill Duke, thinking the person who pilots Grendizer is evil but during the fight Duke necklace falls and the siblings discover who each other is.
Episode 50
Maria the new member on the team, is able to control Grendizer and Marine Spazer. She also has the ability to foresee events so she is able to save Koji from Vegans.
Episode 51
The Vegan plan is to make this moon enter the Earth's atmosphere and cause a catastrophe. The battle between Vegans and Grendizer takes longer than anticipated and it is too late for Grendizer to fire the missile.
Episode 52
General Zuril orders a powerful attack with his latest saucer beast "Domo Domo" to defeat Grendizer before General Dantos gets the chance.
Episode 53
Duke Freed will go after Hikaru who is hostige on foot not using Grendizer and help her escape from the giant beast while Koji takes Grendizer back for repairs.
Episode 54
The Vegan built a base underwater knowing that Grendizer cannot withstand depths great than 400 meters.
Episode 55
Vegans gather some fuel from an industrial island. General Zuril instructs General Gandal on what to do but he doesn't listen and he gets into trouble because his unilateral action revealed that the Vegans have a base on Earth.
Episode 56
Dr. Umon launches a satellite into space to track Vegan movements on Earth.
Episode 57
Koji and Maria are on their vacation in Tokyo, they get into a fight as usual and split up.
Episode 58
The Vegans make a false Grendizer that attacked Earth people so the real Grendizer will be hated.
Episode 59
A group of Vegan kids come to Earth and hold hostages the people inside the observatory.
Episode 60
The Vegans attract a huge number of rats to use for their next mission. These rats are implanted with Vegatron bombs for the purpose of blowing up different targets in Tokyo.
Episode 61
Toko 1, Toko 2, Toko 3, and Toko 4 are Vegan agents taking appearances of other people trying to distroy Space Science Centre.
Episode 62
Swans are implanted with Vegatron missiles for the next Vegan plan. Duke Freed is forced to kill the swans and must head to the city and face saucer beast "Go Go".
Episode 63
Kirika, a Vegan scientist, is sent to freeze with her new weapon Duke Fleed.
Episode 64
The Vegans invent a bomb and General Gandal threatens to blow up Tokyo is Grendizer does not surrender.
Episode 65
The Vegans fire a big group of missiles towards Tokyo. The Grendizer Team launches to destroy the missiles before they hit the city.
Episode 66
Maria in the Marine Spazer gets stuck in a giant seaweed trap and Koji swims to the bottom of the sea to help her.
Episode 67
General Zuril launches an attack on the Space Science Centre with air balloon bombs. Koji gets caught by the Vegans and held as hostage.
Episode 68
A young man from Freed named Kane is a loyal soldier of the Vegans. He comes to Earth to fight. Maria tries to face him and they both crash. Soon she will realize that Kane was her childhood friend from Freed.
Episode 69
The son of Zouril,Zuril Jr. wants to fight Grendizer but Zouril doesn't want him to. Zuril Jr. sacrifice himself for his father in the end.
Episode 70
Maria has a nightmare about her father being hostage. She goes to the cave where she saw her father in her dream along with Koji where she learns the truth.
Episode 71
Moros, Duke's best friend from Freed was made to believe that Duke Freed destroyed Freed by Vega and now comes to Earth to kill Duke.
Episode 72
Princess Rubina, Duke Fleed's fiancé comes to Earth to tell Duke that his planet is no longer polluted but dies after being shoot by one of Vega's generals.
Episode 73
King Vega prepares to attack Earth but Duke and company are ready to stop him with the help of Grendizer and Spazers.
Episode 74
Duke finally destroys King Vega but he and Maria must return to planet Fleed.
