With the destruction of planet Tek, the sole survivor, princess Tekla accompanied by Voxx travels to another system to warn all planets about the Beast Invaders. She crash lands on planet Ice where a quarrel between the Royal legion of King Cryos confronts a Rock expeditionary mining squad, including Graveheart. A Beast cohort launches a full-scale attack and only the Ice sovereign, Graveheart and a convalescent Tekla survive the first purge. King Cryos and his aides heal their former adversary and welcome Graveheart in joining the Alliance. Meanwhile, the Beast Armada invades the system and begins preparations.

The Aurora, Cryos' flagship, travels to planet Rock to convince Lord Mantle to join the Alliance. Sadly, the army arrests Graveheart and the Rock King expels the Ice King determining he is still his greatest enemy. Lord Mantle condemns Graveheart to imprisonment. Meanwhile, Blokk the supreme warlord of the Beast launches an invasion on planet Rock with Voyd permission. Jade, a rock commander and a long time friend of Graveheart, releases him and they run to the Core central to activate the planet's defense – the Battle Moons. They succeed but Lord Mantle banishes the “miner” still not believing in the alliance. Despite all odds, Jade agrees to join them, claiming to need to watch her friend's back.

The Aurora travels to planet Fire in hope of convincing prince Pyrus to join them. The obstacle here is the Grand Vizier who doesn't trust strangers. He orders Graveheart and King Cryos to survive a labyrinth of lava where lava dogs are lethal beasts. Meanwhile, Zera, Cryos' daughter, is furious at prince Pyrus for not intervening but a Beast battalion interrupts their argument and wounds the young lord of Fire. However, Jade arrives at the last moment and saves the children. Graveheart and Cryos survive the test and Fire is pleased to join the Alliance.

The Alliance travels to planet Bone but finds a surprise – the Beast planet is already there. Emperor Femur, an arrogant and egotistical leader, agreed to welcome both the Beast and the Alliance on his world. Lamprey the Deceiver and her agents convince the Bone Emperor to side with them and send on the run King Cryos, Graveheart, Jade and prince Pyrus. The young prince of Fire believes he can reason with Femur but is captured by Lamprey and her warriors. Eventually it is revealed that the field generator built on planet Bone will not protect the planet but will instead seal the entrance to any Alliance Battle Fleets. When betrayed, Femur rescues Prince Pyrus and creates a diversion allowing the Aurora to destroy the Field Generator giving their fleets the chance to swarm the invaders. Bone joins the Alliance. Back at their World Fortress, Lamprey tells Blokk and Voyd that she believes Tekla to be responsible for uniting the worlds.

Lamprey possesses the body of Tekla and intends to crush the fragile Alliance by murdering its leader Graveheart. Her plan fails when she mentions details the real Tekla couldn't know. She escapes inside Femur's flagship heading back to Bone.

Tekla and Lamprey battle for the domination of Tekla's body and spirit. Tekla manages to defeat her enemy and regains control of herself.

Someone frames Jade for murder on planet Fire. On this world the punishment for murder is a death sentence. Graveheart leads prince Pyrus and the Grand Vizier on an investigation and the miner determines the criminal's fingerprints aren't those of Jade. When Lamprey the Deceiver and her warriors appear, there is a battle and the group is rescued by princess Tekla and King Cryos. Jade is free and the heroes have saved the day.

Someone has kidnapped lady Zera, the young princess of planet Ice. It turns out to be Blokk who wants King Cryos to choose between family and duty. If the Ice king chooses family he will have to abdicate the throne. Cryos and Jade rescue Zera while Tekla and Graveheart defend the palace with prince Pyrus and Femur. At the end, the Ice sovereign surrenders the throne to the army commander Medstar.

The Alliance returns to planet Rock to convince Lord Mantle but Tekla fails. Emperor Femur suggests a cunning plan. However, the Bone emperor's intentions are only to steal the Battle Moons for himself. Latter, Blokk orders his legions to swarm on planet Rock while the defensive moons are away. Graveheart and Tekla head to recapture the Battle Moons and save the day in time.

Prince Pyrus and Lady Zera accidentally crash land on planet Remora, a dead world. They must escape Blokk and his millions of warriors.

Graveheart believes he is not the right leader for the Alliance. The miner remembers when his younger brother Mica died on a trip to planet Fire. He failed him. Jade consoles her old friend and convinces him to stand firm.

The assault on planet Remora begins. Cryos is once more sovereign of planet Ice. Bone, Fire and Ice stand against their common enemy. On planet Ice, Tekla and Voxx search for a special weapon underground. Blokk, Lamprey, and Voyd unleash the ultimate power of Remora against their enemies. Blokk fights on and Emperor Femur abandons his comrades leaving them to fend for themselves. Remora fires and destroys half the battle fleets.

The Alliance stands against their greatest enemy. Remora unleashes even more of its offensive strike forces and damages the Ice and Fire battle fleets greatly. In the end, Jade and the Battle Moons rescue the day and it seems Remora is destroyed. However, the Beast Planet shows up and annihilates one of the Battle Moons.

The Beast Planet demonstrates its might, launching an armada to attack Fire while training its powerful cannons on the Battle Moons. A stray blast threatens to destroy Ice, but Tekla and Lady Zera discover world engines hidden within the planet, which move it out of the path of the blast.

The Beast Planet targets planet Fire. Graveheart and Tekla must hurry to find the world engines. During the invasion, Graveheart is injured while saving prince Pyrus. The Grand Vizier witnesses the sacrifice and reconsiders his judgment towards the outlanders. In the end, everything is lost for planet Fire but the Grand Vizier sacrifices himself and tells prince Pyrus that his new friends are indeed worthy ones. Prince Pyrus orders the Vizier to evacuate with the rest of his people, because he still needs his guidance and company. The Vizier disobeys, saying that Pyrus is old enough to rule, and that the Vizier does not want to die a coward. The Grand Vizier uses the world engines to ram Planet Fire onto the Beast Planet's claw, hoping that it will destroy the Beast Planet, The Beast Planet consumes planet Fire anyway, killing the Grand Vizier.

Emperor Femur and Pelvus must make good their commitment to return to the Alliance. They agree to feed all the people of the Alliance with the resources of Bone, and so Bone rejoins the Alliance.

Captain Blaze and his renegade squad steal one of the Battle Moons and attempt to regain their lost honor in destroying the Beast Planet. But when Blokk and his battle fleets almost seize Prince Pyrus, Captain Blaze returns to save his young lord. At the command center, Jade is contacted by Lord Mantle to finish their bargain.

The Alliance travels to planet Sand. Lady Zera meets one of the Sand People, Zuma. She is a telepath. In the end, the great Sand People save the day with their mind power.

Jade, princess Tekla, Lady Zera, Pelvus and Zuma head for "Moon Over Mayhem" to socialize. In an attempt to reconcile, Tekla gives Jade the key of the Cluster defenses. During this pleasure trip they are attacked by Fire's pirates and smugglers as well as Lamprey and her drones.

The Alliance of the Cluster find Planet Jungle. They are willing to sacrifice this non-living world to trap the Beast Planet and Blokk's forces. On a trip to planet Jungle they place explosives but living plants ask for their help. Tekla finds out the planet's world engines were destroyed long ago. The vegetation on this world is doomed. A sentient plant asks Femur to preserve a small part of the planet's life. Planet Jungle explodes, but the Beast Planet is unharmed.

The Alliance is surprised when Planet Fire catches up to them. Apparently the Grand Vizier is alive but his personality seems different. It is revealed that it isn't the Grand Vizier but a creation of the Beast planet. The Alliance retreats into a nebula to evade destruction from Blokk and his battle forces.

The Alliance detects a signal from a mysterious planet which is determined to be a battleground. Graveheart and Cryos are traveling together as are Jade and Femur. The two groups crash land separately and lose contact with their fleet. The miner and the Ice King are found by Jewelia and her band of criminals. Jewelia develops a liking for the former rock soldier. Jade and Femur meet Sternum who is a tough warrior from planet Bone. Sternum relocates the prison planet to another location evading the scanners of any possible enemies.

It turns out the prison planet can teleport itself. Sternum is revealed to have been Femur's brother. Tekla and Pyrus must confront Lord Mantle, who wants to rule the Alliance. Mantle shuts down the defenses for the entire Alliance endangering the fleet. Meanwhile, Jewelia and Graveheart lead an attack on Sternum's camp but are driven off by its superior arsenal. Sternum was the rightful ruler of Bone before being overthrown by his brother and seeks revenge on Femur. Graveheart and Jewelia retreat while Tekla has no choice but to pass over leadership to Mantle. The Rock King reveals a key which is the defense key given by Tekla to Jade. On the prison planet Jade is set to kill Femur.

Both factions of the prison planet prepare for their next battle. Blokk and Mantle engage in battle; Blokk proves victorious and kills the Rock Lord.

The Beast has captured Planet Rock, and starts to round up the planets' population. On the Prison Planet, the fight between the two factions continues, but Graveheart, Cryos, Jade, and Femur are reunited. The Sand people find the Prison Planet and guide the planet back to the Alliance system. The planet teleports back, appearing between the Beast Planet and Planet Rock. As the Beast Planet's claw closes onto the Prison Planet, Sternum activates the teleport engines, teleporting both the Prison and Beast Planets to parts unknown.

The episode opens with Lord Mantle's funeral. As Graveheart speaks and the Alliance watches, Blokk kills three Rock soldiers. Tekla, Pyrus and Zera confront Jade to demand why she would betray them, and Graveheart reveals that it was to convince Mantle to lend them the Battle Moons for the fight with Remora. Graveheart then asks Jade to be the next ruler of Rock. Blokk enters the World Engine and kills all the Rock soldiers except the captain. He steers the planet towards the closest star. He then contacts the Alliance and demands that Graveheart face him. Voxx repairs the world engine allowing Jade to steer the planet away as Graveheart finishes Blokk off by plunging the Forcefield Generator inside him. In the aftermath, Jade makes Graveheart an official Rock citizen, and the series ends with the Beast Planet devouring another planet, the subtitle below echoing the first episode: "Planet Reptizar: On Doomsday".