The Empyrean

The Empyrean is a type of energy transference that some people in the galaxy can perceive and carry out. These people are known as empyrrics, and they operate on the ability to sense sources of empyrric energy (sometimes known as empyrric potential) in others.
Empyrric potential constitutes emotions, sensations, memories and basic life essence.  An empyrric can convert this potential to empyrric energy. When life essence is being used as fuel, whatever is dying to fuel it burns in green flame and disintegrates.

What normal people see is the output. When a keeper attacks, they convert empyrric… call it potential… into empyrric energy. Potential can’t hurt you. Energy can. Nexus lanes? Or Varna, you call them? You see that because it’s energy propelling us along. Maybe. Everatus IV? Those flames were energy.

— Ferrash Progmannae, The Empyrean

The Empyrean, when wielded, most often manifests as green flames, beams, sheets or spheres. It siphons the chosen fuel source into itself to deadly effect. It can be coalesced into a sharp edge for long-distance slicing, it can be used as a shield, it can be used to set things on fire, it can be used to push things. It can also be used to speed the user's movements (though this is complicated enough a feat that it usually only applies to foot movement in a straight-ish line). The most controlled empyrrics can extend their energy a very long way and manipulate several individual tendrils of fire.
Where fuel sources are prepared in advance – like sannots or people wearing pain meshes in The Protectorate and volunteers in The Hegemony – they are trained or programmed to have a certain access trigger. Only the empyrrics they work with know the trigger, so it will be far easier for them to use the energy than another empyrric. Empyrrics can also protect the energy of others to some extent by placing a thin screen in front of them that hazes the emotions behind it. This technique is less effective for The Keepers, as they rely strongly on pain, so the pain meshes' in-built triggers are more useful there. In general, pain meshes' triggers are far more difficult to bypass than anything trained.
The Empyrean is a blunt instrument. It is not subtle. It most often causes more harm than its user intended. Battles between two empyrrics tend to come down to who is most able to manipulate their own emotions or who can field the most fuel sources whilst guarding them.
Common pitfalls with beginners are emotional overload, where the user's emotions build to a point where their present abilities can no longer contain them. This results in spontaneous combustion and significant damage within a large local radius. This can be avoided by gradually siphoning off the power or by bringing the emotions under control.