When activated by a character with Dark Knight as a support job, each successful attack that lands will cause the user to lose 10% of his/her maximum HP and converts half that amount directly into damage.
The damage penalty of Souleater is NOT affected by Defense or VIT, Damage Taken+/-% such as Defending Ring(-10%), the Red Mage spells Phalanx or Phalanx II, -% Physical Damage Taken gear such as Earth Staff/Darksteel armor, -% Magic Damage Taken gear such as Coral Scale Mail, nor is it affected by the Paladin ability Sentinel.
The damage penalty of Souleater can be nullified by Stoneskin for an amount equal to the HP equivalent that the Stoneskin provides.
Souleater is subject to physical damage modifiers, examples being open-mouthed Hpemde(+100% damage), and Slimes(-50% damage); additionally the modifiers for damage type (slashing, blunt, or piercing) based on the weapon used will affect the damage dealt by the ability--e.g., Skeletons take extra damage from Souleater when used with a Club.
While active, this ability increases the user's accuracy by 25.
When activated and while active, a large amount of enmity is added to user.
HP converted into damage for a weaponskill is calculated before the weaponskill itself. For example, a Dark Knight using Guillotine will convert 40% of their HP into damage, since it's a four-hit weaponskill, rather than the ~34% it would of been had the four hits been separate (and assuming no healing in between hits).