There was a time, in Star Wars' Legends lore, when Tattooine was an oasis covered in oceans that teemed with life. The tides fell on azure bays, whose pools coursed into blue rivers that fed lustrous cities. Then the Infinite Empire came, collected the planet's Force-sensitives, and plundered Tatooine's resources to fuel their ambitions. Those incursions not only led to the terraforming of a lone world in the Outer Rim but also the transformation of the entire galactic core and the shaping of the ancient common ancestors of the Jedi and Sith.
The Rakata were disciples of the dark side who achieved status by amassing slaves, wealth and Force adepts. Some of those chosen few were called Force Hounds, specifically bred in thrall to their masters to prospect Force nexuses. The planet Tython, homeworld to Force devotees called Je'daii, was one such nexus, and the collision of these two cultures led to radical dogmatic changes within the nascent order and the adoption of their signature weapon: the Forcesaber.
Forcesabers Could Only Function When Powered by Dark Emotions
Rakatan technology was advanced and included ships and weapons powered by the dark side. A boy named Xesh was steeped in the dark side at a young age, cultivated by its devotion to anger and ruthlessness, and taught how to funnel his proficiency with those energies into the Rakata's alchemical tech. Eventually, a Predor named Tul'kar noticed his abilities and trained him as a Force Hound. The weaponry of the Hounds was also powered by the dark side: a blade of frozen energy called a Forcesaber, which contained a synthetic ebony crystal in its hilt. Xesh and his master were summoned by Predor Skal'nas to chart a path to a hidden planet strong in the Force, Tython.
Tython, a world that responded to the ebb and flow of the Force, had been isolated from the rest of the galaxy for 10 millennia before Xesh crash-landed there. The dark side energies he brought with him created maelstroms of wind and lightning that threatened the stability of the entire planet. Emerging from the wreckage of his escape pod, Xesh ignited his saber and quickly shattered the durasteel blades of the three journeymen Force warriors who confronted him. After a council of Je'daii quelled the storm and exiled the Hound to one of the planet's two moons, they examined his weapon in detail.
Lacking an ignition button, the blade could only be summoned by pouring dark emotions into the embedded crystal, something the isolated Je'daii were almost incapable of due to their single-minded pursuit of balance within the Force. As opposed to lightsabers that were forged in harmony with the Force and its wielder, Forcesabers demanded a sacrifice of serenity. Only aggression and hostility kept the blade alight, so one had to continuously exist within a state of practiced rage to harness its incredible power.
The saber itself was no more powerful than the swords it would come to inspire, but the concentrated application of hate made even its kindling a foregone conclusion to bloodshed, which also meant that it could tempt its wielder irrevocably to the dark side. The danger lies not in the weapon itself, as much as in the temptation it represented as a path to fear, anger and hatred. The Je'daii who had maintained a balance within the Force were tainted by their exposure to the Forcesaber, and nothing would ever be the same again.