Inner fire is the measure both of rage and of control, and the substance of Barbarian heart and guts; in purity, it fuels the bloodlust of the battle-hardened and stills the mind of the meditator. But be wary - the taint of magic will disrupt this fragile balance of body and soul, so leave the mana-meddling to those who lean on magic as a crutch!
What little is known is that there is an anti-magic power source, ostensibly called the Inner Fire, that can affect limited subversion of reality. It's not magical in the technical sense (it does not involve the manipulation of mana, its practitioners do not undergo Attunement, etc.), but it's certainly "magical" in the sense that it does something that the uninitiated consider impossible in their understanding of the world.
Creating the subversion seems to require either a strong emotional prompt (Barbarians) or an altered state of consciousness (Barbarians and Thieves). Some scholars have pointed out that this is frighteningly similar to what happens to a magician who is casting a sorcery, but no distinct relationship has been formed. 
Levels of inner fire
- a brilliant aura of pristine quality burning outward at twice your height
- a brilliant aura of beautiful flames extending nearly twice your height above your body
- a brilliant aura of beautiful flames extending a little more than one and half times your height above your body
- a brilliant aura of flames that extends over your height again above you
- a brilliant aura of flames that extends nearly your full height again above you
- a brilliant aura of beautiful flames extending a little over half your height again above you
- a brilliant aura of beautiful flames extending out around you about half again your height
- a bright aura of beautiful flames extending out around you just beyond the reach of your arms
- a bright aura of beautiful flames extending a quarter of your height above you
- a bright aura of beautiful flames
- a small aura of beautiful flames
- a tiny aura of beautiful flames
- a dim glow as if a flame lurked just out of sight
Inner fire pool
A Barbarian's Inner Fire pool never actually grows as the character grows. Instead, as circles are gained abilities become more efficient, requiring less Inner Fire to use.
Regaining inner fire
Inner fire can be regenerated actively as well as passively.
- Active regeneration
- Landing a killing blow.:ALL kills award some inner fire. 100% of this inner fire is awarded if the kills are exactly 120 seconds apart. If they occur closer, the IF awarded will be determined by the % of time elapsed.
- Completion of the Analyze Flame Barbarian ANALYZE Combo.
- A chance to regenerate some Inner Fire when using a CCM Combat Charged Maneuver if an Expertise skill check is passed.
- Smashing or Eating runestones or spell scrolls using the MEDITATE command. There is a tiny chance that destroying items will tank your IF, and a small chance of it negatively impacting it. A large chance of a minor IF gain and a tiny chance of a large IF gain.
- Passive regeneration
- Inner fire refills passively to around a third of your capacity. Beyond that you’ll need to refill it actively.
Losing inner fire
Losing inner fire can be the result of several facts. Generally, they are either through use of a Barbarian ability that is fueled by Inner Fire, or through an activity that would sap a Barbarian's confidence in themselves.
- Activating a Meditation
- Activating a Berserk
- Berserk pulse which breaks webbing or a stun
- Using FLEE
- Using MEDITATE on a magic item and failing the check
- Failing to resist magic (This has been disabled)
- Dying will completely extinguish inner fire
Due to a bug where repeated casting of certain area of effect spells (such as Earth Sense) by high level mages can tank a Barbarian's inner fire pool to the point where it takes hours to regenerate, GameMaster Aurdun has removed Inner Fire loss due to failing to resist spells.