Transformers: Armada and Energon
This summary assumes the events of the Linkage manga as in-continuity.
Having been defeated in battle by Omega Supreme, the evil demi-god Unicron was reduced to a state of near-dormancy, and, disguised as Cybertron's moon, began a new plan. Cybertronian history is unclear on exactly what happened next - apparently, the planet suffered a mysterious cataclysm that predated the appearance of the Mini-Cons. Presumably, this was Unicron's doing, as it would eventually be revealed that he had implanted some of his cells within Cybertron, where they were cultivated and hatched into the Mini-Cons. Bearing witness to this birthing, however, were Rad, Carlos and Alexis, three human children who would befriend the Mini-Cons a million years hence, who had been temporarily displaced in time. By coming into contact with the Mini-Cons at this early, raw stage in their evolution, they planted the seeds of souls, sentience and feelings into the robots, telling them that they would be waiting for them on Earth.
And so, the Mini-Cons emerged on Cybertron, and their ability to enhance the strength and power of the larger Transformers soon became apparent. This had, of course, been Unicron's desire - as the Autobots and Decepticons clashed over the Mini-Cons, the negative energies of hatred and war fed Unicron, slowly regenerating his body. It is unclear, however, whether or not the war had actually existed prior to the coming of the Mini-Cons, or if their presence actually began it - it is worth noting that rather than simply being caught in the middle of events, the Mini-Cons genuinely seem to corrupt and induce a desire for combat in some beings (as would later be evident with Atlantis).
Eventually, the Mini-Cons developed full sentience and desired to leave Cybertron, to find Earth in accordance with the memory that had been planted in them at the moment of their birth. The Autobots aided them in this endeavour, while the Decepticons attacked, but failed to stop the Mini-Con craft Exodus from escaping through a trans-warp portal. The Mini-Con ship was crippled, however, and upon emerging through the portal in the vicinity of Earth, began plummeting towards the planet. The ship first impacted with the moon, and was torn in two - the rear portion of the ship remained lodged on the moon, while the forward portion crashed on Earth. The ship's entire Mini-Con crew were rendered trapped in the suspended animation they had placed themselves in, sealed in small panels, many of which had scattered all across the face of the Earth as their craft entered the atmosphere. The fragment of the ship on Earth was buried in a mountain, and lay there untouched for a million years.
In the interim, some ancient civilisations came into contact with some Mini-Cons. One Mini-Con panel was found in the desert, and apparently used in some way to fashion a temple, filled with advanced-technology booby-traps. More notably, the three Mini-Cons that comprised the Star Saber sword were found and freed by the civilization of Atlantis, who used the Saber as a power source (which would historically be recorded as orichalcum). But the power of the Mini-Cons corrupted Atlantis, and they went to war with another race, who had apparently gained control of the Skyboom Shield Mini-Cons. The resultant energies released in the battle sank Atlantis, and resealed the Mini-Cons, scattering them once more, save for one that remained in the sunken city.
In the Earth year 2010, the crashed Mini-Con spaceship was discovered by Bradly "Rad" White and his friend, Carlos Lopez, while they were exploring the caves outside their city. The inadvertently reactivated the ship, which sent out a signal that reactivated the Mini-Con panels across the world (allowing them to be tracked, not freeing the Mini-Cons within), and reached Cybertron, alerting the Autobots and Decepticons to this development. Megatron, Optimus Prime and their forces soon arrived on Earth, as Rad, Carlos and their friend, Alexis freed and befriended the Street Action Team (but it was, of course, no coincidence, as they had already imprinted on the humans, having met them in the past). The Autobots and Decepticons soon took on Earth forms to disguise themselves, and set up bases in the fragments of the Mini-Con ship on Earth and on the Moon, respectively.
The hunt for the Mini-Cons began, with each member of the teams first acquiring their partner Mini-Cons. Each Mini-Con has an in-built servility program that bonds them to the Transformer which awakens them from their panel, or with whom they combine, which makes them subservient to them. However, if the partner respects the Mini-Cons free will, there is little to no negative effect - such is the case with the Autobots. The little robots are incapable of true speech, communicating only through bleeps and whistles, although certain human beings are attuned to the same mental wavelength as the Mini-Cons, allowing them to telepathically perceive their speech - such was the case with Rad, Carlos and Alexis.
The next target for recovery was the Star Saber sword, but, unbeknownst to anyone, however, the Star Saber was one of three Mini-Con weapons which Unicron had crafted as keys that would reawaken him when the time was right. From his own body, he created an agent named Sideways, whom he sent to Earth to manipulate events, escalating the conflict to feed him further, and also arranging the Mini-Con weapons into position so they could be easily claimed. Following the successful formation of the Star Saber, the next target became the Skyboom Shield, which was successfully acquired by the Decepticons, who had also managed to steal back the Star Saber, thanks to Sideways's treachery and side-switching. In the ensuing battle, however, the Skyboom Shield fell into Autobot hands, and when it and the Star Saber met, an incredible energy flare was released as the two objects' powers fused momentarily.
While all these events were occurring, other Mini-Cons had awoken on their own in other parts of the world. One such group, the Super Stunt Team - working with Stella, a human female with the mental attunement - soon fell afoul of more of Unicron's agents - the Speed Chaser Team, Mini-Cons who had surrendered to Unicron and were more powerful as a result. The battles that followed also saw the Sonic Assault Team pulled into the conflict, and the power exhibited by their foes prompted Redline of the Super Stunt Team to begin experiments into achieving this upgrade for all Mini-Cons, while allowing them to retain their free will. They established contact with the Autobot Mini-Cons on Earth, telling them to prepare.
With Sideways's status as a double agent and a manipulator revealed to the Decepticons, he was dispatched from their ranks, displaying his incredible Unicron-born powers by reshaping his body after being destroyed by the Star Saber. He proceeded to inform the Autobots of the existence of the third Mini-Con weapon, the Requiem Blaster - a newsflash that came just as the giant Decepticon warship, Tidal Wave, arrived on Earth to make life difficult for the Autobots. Rad, Carlos and Alexis succeeded in locating Skyblast, one of the Blaster's components, who overcame his fear of conflict to perform a stunning fear - in the midst of battle, Skyblast unleashed a beautiful, electronic harmony, a song which awoke the other two Mini-Cons and called them to him. They combined into the blaster, which was briefly held by the Autobots until the Decepticons invaded their base, stole it, and killed Smokescreen.
Subsequently, the Decepticon Starscream was abandoned by his teammates, and joined the Autobots in a misguided attempt to claim revenge on Megatron. Providing them with access codes to the Decepticon base, Starscream participated in an invasion which revealed that Megatron was using all the captive Mini-Cons to construct a starship that would return them to Cybertron. Perceptor attempted to make the Mini-Cons stop, but they would not listen until Megatron assaulted Perceptor, at which point all the Mini-Cons ceased working, turned on Megatron, and once again sang their beautiful harmony. In the course of ensuing events, Starscream and Megatron battled with the Star Saber and Requiem Blaster, another flare of energy being released as two of the three Mini-Con weapons met. The Autobots successfully saved all the Mini-Cons from the Decepticons, but the seed of doubt had been planted in Starscream's mind when Optimus prevented him from killing Megatron.
Starscream was then manipulated by Thrust - who was in turn being instructed by Sideways - into returning to the Decepticons, stealing the Skyboom Shield from the Autobots, thereby giving the Decepticons ownership of all three Mini-Con weapons. Locked in their weapon forms, the weapons were used as a mighty new weapon, releasing the energy as they had done before when brought together, this time controlled by their integration into the new weapon mounted on the front of the new Decepticon starship, the Hydra Cannon. The Decepticons launched and targeted Earth with the cannon, but Optimus Prime absorbed the blast with his Matrix, sacrificing himself to save the planet.
Meanwhile, Redline had successfully unlocked the Master Key, bestowing upon himself, and gradually all other Mini-Cons, the enhanced, unrestrained powers that Mini-Cons normally do not have access to. With these new powers, he and his allies were successfully able to defeat Ravenus, another of Unicron's agents, who had been instructed to destroy the Linkage, the communal mind of all Mini-Cons. With the Mini-Cons' full powers now unlocked, all the remaining robots joined the Autobots in their pursuit of the Decepticons, back to Cybertron.
Being parts of Unicron, the Mini-Cons possess a wide array of powers. With their abilities unlocked, they perpetually glow with a green aura, and are able to communicate verbally. They possess enhanced strength, energy projection powers, are capable of interstellar flight, and can upgrade and repair other Transformers by bathing them in their light - Hot Shot, Red Alert, Demolishor, Starscream and Megatron (now renaming himself Galvatron) received such upgrades after their defeat at the hands of Nemesis Prime. The Mini-Cons were even able to resurrect Optimus Prime by entering the Matrix and forming a new body for him. They also created Overload in this manner.
When both forces subsequently returned to Cybertron, Sideways and Thrust succeeding in stealing the Mini-Con weapons - when Starscream and the kids pursued Thrust, High Wire used his powers to initiate the time displacement that sent Rad, Carlos and Alexis back in time, triggering events. After they returned, Thrust and Sideways brought the weapons to Unicron, reactivating him, and as the planet-eater turned on Cybertron, the Mini-Cons merged their bodies together, forming a duplicate of the dark god, and grappled with him hand to hand, until Unicron exerted his influence over his creations, turning them back into his servants. He absorbed Galvatron and the children into himself, but with their consciousnesses integrated into his, Rad was able to awaken High Wire once more, that effect spreading to all the Mini-Cons, who penetrated Unicron's body and bathed his interior in their light, awakening the weapons and cutting off Unicron's power, leaving him deactivated in space. However, he soon began to move again as Galvatron began a fierce battle with Optimus Prime, which only ended when Galvatron sacrificed himself to stop Unicron.
Over the ensuing ten years, Mini-Cons became much less of a desired commodity as the Autobots and Decepticons worked together with humankind to establish cities on Earth and in the solar system to mine of the energy-rich mineral, Energon. The Street Action team received upgrades to their bodies, but rarely saw any kind of combat, content to partner around with Kicker. The Energon Saber Mini-Cons - apparently not upgraded Star Saber Mini-Cons - were stationed at Mars City, and survived the devastation there, joining the fight against Alpha Q and his Terrorcons, wielded as a weapon by Ironhide and Kicker.
Read more about this topic: Mini-Con, Anime Series