In the near future, a secret society, Nematoda, with ambitions of world domination, hired three men, Professor Akitsu, Professor Himuro, and Professor Wakatsuki, to build the ultimate "G-Class" giant robot, Hades Project: Zeorymer. Nearly two decades later, on his deathbed, Professor Akitsu tells his son, Masaki Akitsu, that Zeorymer must not awaken. A short time later, a new student transfers into Masaki's school, named Miku Himuro. She quickly persuades him to meet her adopted father, Professor Himuro, and Masaki is curious to find out what is going on, and what his father meant in his final words. Traveling by a high-speed pod hidden under the city, he meets Professor Himuro in a vast underground facility. Nematoda's General Golshid, aware of the Himuro's appearance in Japan, send a G-Class robot to assault their base and kill them, as they believed they had the only "Joint". Himuro compels Masaki to pilot Zeorymer and save them, as he is the only one that can pilot it. Once he agrees, Himuro and his daughter head to an operating room without Masato's knowledge, and he installs a sphere called a "Dimensional Joint" - a flawed duplicate of the original - into his daughter's womb, and she is teleported to within Zeorymer's "eye". This is necessary to utilise Zeorymer's true abilities - without them, it is simply an outdated G-Class robot. Though Masaki stumbles with the unfamiliar systems, Zeorymer eventually awakens fully, Masaki undergoes a strange and short-lived shift in personality, and with the spherical energy weapon on the back of Zeorymer's hand, destroys its opponent in a single attack.
Soon, Nematoda sends its three newest and most powerful robots after Zeorymer. Finding its pilots at school, they attempt to apprehend them, but Zeorymer is teleported to their location. Masaki's personality shifts again, and Zeorymer fights the three, despite being in the middle of a city, showing no care for civilian casualties. Zeorymer shows its power, being much faster than the fastest of the three, vastly stronger than the strongest of the three, and takes the many, many missiles of the third without damage. Finally, Zeorymer activates both of the spheres on the back of its hands and taps them together, the shockwave cleaving the final robot and several buildings behind it in two. As a result, the city has undergone immense damage, and many of its citizens are surely killed, including all of their schoolmates.
With Nematoda, General Golshid, seeing the vast power of Zeorymer, elects to pilot the powerful Rose C'est La Vie, a G-Class robot that had crippled test pilots, even at less than full power. Knowing he has little choice Golshid still elects to go, with Rose C'est La Vie at full power. Upon returning to base, Professor Himuro is shown to have collapsed and is dying of an incurable disease, and Masato realised the level of destruction fighting would cause, but strangely didn't care. Suddenly teleported to Zeorymer's cockpit, it's revealed that Masaki is the revived, evil, Professor Wakatsuki, reduced to an embryo and reborn to escape an inevitable death, Miku was Himuro's wife, who had been cheating on her husband with him, had undergone the same process as she had been caught in the same event, and that Himuro was the one to attempt to kill them. Though the three scientists were conspiring against Nematoda while they worked for the organisation, Wakatsuki was planning to betray the others and take Zeorymer for himself. Akitsu and Himuro had stolen the embryos to stop the revival, and Akitsu then took Masaki's embryo and fled from his other colleague as well. However, by activating Zeorymer, the memories and personality of Wakatsuki had been installed into Masaki, though the same was not true of Miku. Following this reveal, Wakatsuki forces himself on Miku, sexually, and uses sex to make her his.
Rose C'est La Vie lands and fights Zeorymer. Golshid successfully tears off one of Zeorymer's arms, but it is instantly regenerated in its entirety. He then successfully destroys its cockpit, killing Wakatsuki, to which both cockpit and pilot are regenerated completely. Defeated and nearly destroyed, Golshid is saved by the sudden loss of power of Zeorymer, as the Dimensional Joint had finally failed. With both robots retreating, Wakatsuki installs a new Dimensional Joint into Miku, and upon her awakening, suddenly shifts back to Masaki for a moment. With both Wakatsuki and Miku realising, Wakatsuki reinforces himself and flees. In the midst of coitus with Miku, Masaki comes to the realisation that the "fake Masaki Akitsu" was not a fake - it was not Wakatsuki's personality that was installed, just his memories. While that would be enough for a child without memories to become a "true" Masaki Wakatsuki, Masaki Akitsu's personality was too strong, and he eventually came to the realisation that he was simply being dragged along by how he thought he should be acting, thanks to Wakatsuki's memories, with Professor Himuro secretly watching. Deep in the base, Himura hovers over a switch, which would destroy the flawed Dimensional Joint in Miku's womb, killing both Miku and Masaki, but accepts that Masaki is not really Wakatsuki, and Miku is not his deceitful wife, feels guilt for considering Miku to only be a tool, and dies of his sickness. Upon finding him, Masaki decides that the only way to escape Zeorymer is by burying it himself, and decides to do so by attacking Nematoda's main base.
Arriving at Nematoda's base, Zeorymer's landing destroys many of its defending machines with the resulting shockwave, and makes short work of the remainder. Suddenly, the president of Nematoda appears, piloting a black Zeorymer, powered by the original Dimensional Fault installed into an "inhuman" Miku clone, revealing himself to be a second backup of Wakatsuki, but one with advanced aging thanks to the destruction left by the theft of the original Zeorymer affecting his regeneration. After the theft, he had killed the Nematoda president and taken his place. Fighting with Zeorymer and showing that they had equally powerful offensive and regeneration abilities, the two Zeorymer grappled and began to merge. Revealing that Zeorymer's power source was in another dimension, and that as a result, there can only be one Zeorymer, which was the reason that even Masaki couldn't make a perfect Dimensional Joint, despite having Wakatsuki's memories, the two machines merged into one, with the fake Miku collapsing, the original Dimensional Joint installing itself into Miku's womb, and Wakatsuki planning to take over Masaki's body in the process. Though Zeorymer is merged into a half-black, half-white version, Masaki, Miku and Wakatsuki were ejected from it. Wakatsuki fails to understand why, but Masaki enlightens him - Zeorymer reformatted its pilot registry when Masaki started piloting Zeorymer, and was installed with Wakatsuki's memories. Thus, Zeorymer couldn't install Wakatsuki's personality into Masaki's body. Wakatsuki's driven somewhat mad, reveals that he also has a self-destruct for the Joint in Miku's womb, but is shot and killed by Golshid, furious at Wakatsuki's murder of the original Nematoda president. However, there's a massive Deuterium Bomb under the Nematoda base, activated by Wakatsuki's death, which is large enough to destroy the world. However, Zeorymer is strong enough to survive. Rather than escaping, Masaki and Miku plan to absorb all the energy from the bomb's detonation into Zeorymer and into the other dimension. Golshid's expectation is that even Zeorymer will be destroyed, but Masaki says that he and Miku want to live, in this world that they grew up in. As they attempt it, Golshid is shown to have escaped in a pod. Though Masato and Miku succeed, the manga concludes by saying that no-one ever saw the G-Class Robot "Hades" ever again.
Set in the near future, a secret feudal monarchy led by an empress and named 'Hau Dragon' (鉄甲龍[ハウ・ドラゴン], Hau Doragon, literally Iron Helmet Dragon) uses, as a front, a firm 'International Electronic Brains' and has built a set of eight giant robots, each possessing a power based upon the eight elements of earth, fire, water, air, thunder, mountains, the moon and the heavens. However, one of them, Zeorymer of the Heavens, has been stolen and the main character, fifteen-year-old Masato Akitsu, is forced into piloting it with a mysterious girl named Miku Himuro.
Zeorymer possesses an energy based weapon called the "Dimensional Coupler Cannon" that appears almost telekinetic in nature; by holding its fist in the air, or aiming it at a target, energy strobes across the orb and causes a large explosion to engulf whatever enemy it is directed against. These orbs can also fire beams of golden-hued energy (labeled as the Energy Wave attack) which can cause massive damage, and project a forcefield which seems nearly impenetrable. The robot itself is also incredibly durable: in the third episode, it was struck with a weapon that left an effect similar to that of a nuclear warhead, yet suffered only minimal damage. Zeorymer of the Heavens is able to hover, fly, teleport unspecified distances, and possesses an incredibly potent weapon known as the Hades Attack (メイオウ攻撃, Meiō Kōgeki): when it lifts its arms in the air then lowers them across its chest, slamming its fists together or against the large golden orb on its chest, the robot releases a huge blast of golden energy that, at full power, can cause an explosion visible from space (inferring the power of several gigatons at least, though even on lower settings this final weapon seems equal to most nuclear weapons in scale). When this attack is activated, a mysterious voice, possibly Zeorymer's itself, can be heard saying "Meiou," the attack's name.
The first of the seven remaining Hau Dragon robots Zeorymer faces is the air-based robot known as Lanstar of the Winds, piloted by Taiha, the lover of Hau Dragon ruler Yuratei. Lanstar is smaller in build but slimmer than Zeorymer, denoting less overall protection but seeming to exhibit greater speed and agility, though they appear to be the same height. Lanstar of the Winds has a pair of huge mechanical wings on its back which seem to be the source of its powers, which are focused around creating and controlling intense air currents. To this end it can generate, at will, "sharp" planes of wind, tornadoes, or even release its signature Dead Long Fuun attack wherein Lanstar projects four streams of incredibly intense air currents that combine into the shape of a serpentine dragon. This intense wind blast creates a vortex of wind so powerful when it strikes a target that it was easily capable of stripping stone and earth from the ground and even causing some damage to Zeorymer's armor.
The second and third robots encountered by Zeorymer were Breist of the Fire and Gallowin of the Water. They were piloted by two identical twins, who seemed to despise one another, much like water repels fire, though it is the "fire" sister Shi-Aen who is more level-headed and controlled while her "water" sister Shi-Tau is hotheaded and untamed. Both Briest and Gallowin possessed what appeared to be several unspecified energy weapons - most of which were left unnamed - though they boasted two incredibly powerful combo attacks: Twin Lords and Twin Flare. The former had them use their primary weapons (Gallowin's twin particle beams, the Beam Searchers, and Briest's shoulder mounted Magna Flares) which are fired at one another. When they impact they result in what can only be described as a huge nuclear detonation capable of tremendous damage; next to Zeorymer's final attack it is one of the most powerful seen in the series. The latter attack, Twin Flare, is when the two robots link into one another and form twin beam cannons which, while powerful, pales in comparison to the Twin Lords attack.
The fourth Hau Dragon robot to attack was Rose C'est La Vie of the Moon, who was piloted by Ritsu, an asexual man who hid his woman-like face behind a steel mask. Rose C'est La Vie was among the most powerful single combatants ever seen in the series and was easily the most powerful Hau Dragon robot besides Zeorymer of the Heavens itself. Rose C'est La Vie was literally loaded with weapons: his chest contained four beam cannons, one beam cannon was hidden in each leg, each of its ten fingers could fire a beam of energy, and when all ten on each hand were combined they formed the Moon Beam Swords, twin energy blades powerful enough to cut through seemingly anything. Finally Rose C'est La Vie possessed a weapon which rivaled even Zeorymer's final attack, known as the J-Kaiser. Parts of Rose C'est La Vie's armor would disconnect and form a gargantuan energy cannon, and three small pods were launched into orbit. They would beam energy down to Rose C'est La Vie, which would project it out as a blast of energy from the J-Kaiser cannon so powerful it left huge craters in the ground and could even shoot a hole through mountains
After three failed attempts to destroy Zeorymer, Yuratei finally dispatched her last three remaining robots: Omzack of the Thunder, Dinodilos of the Earth, and Burrstone of the Mountains, piloted by Saiga, Rokfel, and Giso respectively. Giso seemed to have strong feelings for Rokfel, but she seemed to have similar feelings for Saiga. Saiga was, in turn, a sociopathic man who cared for little other than proving himself the most powerful of all and boasted that his robot Omzack was the strongest Hau Dragon machine ever, which would later end ironically for him.
Their three robots were only featured briefly in the fourth and final episode and so they were not well understood, though some things were made clear: Burrstone was a heavy support robot who mounted over five hundred missiles in various launchers, ranging from normal cruise missiles and guided weapons to hugely powerful atomic bombs capable of destroying several miles of landscape, and also seemed to be incredibly well-armored with huge plates covering its entire body. Dinodilos's powers were ill-defined but it appeared have the ability to, by inserting its huge arms into the ground, control underground magma flows causing geysers of magma and huge earthquakes, and could also have limited control over earth itself. Omzack's powers, despite Saiga's boasts, are in fact never fully shown; while it handily destroyed an entire carrier group in a single massive explosion and was said to possess the "photon lightning system", Omzack of the Thunder proved an utter failure in battle because of Saiga's overconfidence and short sightedness.
The Hau Dragon possessed at least one other mecha - their own flying fortress - but it seemed to be rather helpless without the seven robots to defend it.