The Metanecrons represented a military force composed of genetically altered cybernetic organisms—often called technobeasts—brought into existence by the Sith Master Belia Darzu during the period of the New Sith Wars. Utilizing Sith sorcery and mechu-deru, the Sith Lord Darzu engineered this army through the use of a nano-virus known as the nanogene spore. Within a secret base located on the world of Tython, living beings from various species were forcibly integrated into the Dark Lord's fighting force. As the leader of a revived Sith order, Darzu unleashed her technobeasts against the Galactic Republic and the Jedi Order during the conflict known as the Sictis Wars. The termination of the Dark Lord at the conclusion of this era brought an end to the creation of these mutated hybrids, thus crippling her cyborg army. Many years afterwards, the remaining bulk of Darzu's technobeasts remained within her fortress on Tython, only to be completely destroyed by the Sith Lord known as Darth Bane.
Around 1250 BBY, a female shapeshifter named Belia Darzu took on the title of Dark Lord of the Sith, becoming the leader of a re-emerging Sith group during the Draggulch Period. At that time, Lord Darzu used a secluded stronghold on the world of Tython to conduct experiments in the creation of part machine, part biological creatures referred to as technobeasts. By investigating Sith magic and the Force ability of mechu-deru, Darzu developed the nanogene spore, a nano-machine virus capable of permanently transforming living individuals into Sithspawn mutants. Within the stronghold of Tython, living subjects from a variety of species were subjected to the effects of the virus, including human-like beings, rancors, and banthas. Those infected by the nanogene spore were incorporated into a fighting force of technobeasts known as the Metanecrons.
The technobeasts of Belia Darzu were created for war, equipped with arm-mounted saws and skewers, as well as laser cannons and protective hides. Furthermore, the creatures could spread the nanogene spore themselves, infecting other beings with the virus and generating more hybrids as a result. Empowered by the dark side of the Force, the technobeasts were controlled by the will of Belia Darzu and housed within the living quarters of her fortress. The Metanecrons served as the vanguard of the Dark Lord's forces during the Sictis Wars, a two-decade long segment of the broader New Sith Wars. During this period, the technobeasts were unleashed upon the Galactic Republic and the Jedi Order, becoming recognized as the primary menace of the Sictis Wars. By the final year of this conflict, Darzu's army was crippled following her murder by the clandestine Mecrosa Order, bringing an end to the creation of her Sithspawn hybrids.
Many generations following Belia Darzu's demise, the surviving members of the technobeast army continued to occupy her fortress on Tython. Without their creator and leader, the mutants roamed aimlessly through the halls of the stronghold. Over time, the creatures suffered from the long-term damaging effects of the nanogene spore, becoming deteriorated and malfunctioning. Additionally, they were drawn to the dark side energy emanating from the holocron of Belia Darzu, the last vestige of the Dark Lord's power. Driven by a basic instinct to obey their mistress even after her death, the technobeasts gathered around the holocron within the underground inner sanctum of the fortress.
In 990 BBY, the remnants of the technobeast army were discovered by Darth Bane, a Sith Lord who sought Darzu's holocron to learn the secrets of constructing such a device himself. While the creatures initially ignored Bane, they immediately attacked the Sith Lord when he attempted to take the holocron of their deceased mistress. Despite overwhelming Darth Bane with their superior numbers, the mutated cyborgs were unable to penetrate the defenses of his orbalisk armor. Furthermore, their attempts to infect the Sith Lord with the nanogene spore were unsuccessful; the orbalisk parasites on Bane's armor eliminated the virus from his body. Despite their relentless aggression, the remaining technobeast army was ultimately destroyed by Lord Bane.
During the time of the Yuuzhan Vong War, the technobeasts of Belia Darzu were briefly mentioned in Droids, Technology and the Force, an essay authored by Jedi Master Tam Azur-Jamin.
The technobeasts of Belia Darzu were initially mentioned in an adventure concept—The Lost Art—featured in The Emperor's Pawns, an article published in 2001. However, the creatures were unnamed and unrelated to Darzu at that point. The technobeasts and their connection to Darzu were later identified as such in Droids, Technology and the Force, a Hyperspace fan club article released in 2005. In a later article called Evil Never Dies: The Sith Dynasties, the technobeasts created by Belia Darzu were called "the Metanecrons". The technobeast army first appeared in Darth Bane: Rule of Two, the second book in the Darth Bane Trilogy.