The Embers were a cult that worshiped a ‘goddess’ called Val. She was an embodiment of destructive psionic power.
Several thousand years ago before the League of Systems the Val system was discovered by explorers. They found a complex of ancient ruins on the planet Ember. About the time of the founding of the League of Systems a religion formed which worshiped the goddess Val whose temple was found in the ruins. Only psionics were excepted into their priesthood though worshipers did not need to have psionic powers.
Eventually hearing of the practices of the Embers the Esper Knights visited the planet in force and attacked the worshipers. They tried very hard to wipe the Embers out, going so far as to quarantine the system and blacklist in the League’s official planetary codex to make it hard to find.
However they failed to crush all the Embers and ever since they would encounter pirates, thieves, and bounty hunters who identified themselves as Embers. Some who had remained bitter and hateful towards the Esper Knights helped the Galactic Empire hunt down knights. However the Galactic Empire may have accepted their help, but would betray them in the end as well.
The Embers are a religion as much as a psionic tradition and all it’s members worship the goddess Val. In Val’s image they focus on the destructive potential of Psionic power, caring little for any pain or suffering their actions may cause others. In fact often inflicting pain is the sole reason for their actions.
Fighting with both powers and body are aspects of the Embers training, though the focus is always strongest with offensive psionic powers. Any psionic power that can be used offensively are common to Embers, whether this is psychokinesis, ergokinesis, or others.