Ordinarily the sword functions as a normal weapon with Good bonuses to damage and accuracy. When drawn in the presence of another demonic being Demonsoul's true nature is revealed. The weapon contains the energies of a demonic being trapped within its matrix. When confronted by another demonic being the sword gives off a continuous piercing scream as the blade begins to glow with an eerie purple light. In this state the weapon has the following characteristics:
- Great bonus to damage and accuracy.
- It negates any special attacks (natural energy attacks, ability drains, mind control attempts, spells, etc.) used by the opposing demon, absorbing any energies directed at the wielder.
- The sword's damage and accuracy bonuses rise to Superb.
- The wielder gains Superb physical toughness, reducing all physical damage received by two ranks.
- The possessed becomes immune to fire, electrical damage.
- The possessed gains immunity to mental attack forms (except, of course, being possessed).
- Demonsoul continues to absorb demonic attacks directed at the wielder.
Should the demonic foe be defeated before the wielder recovers from possession the demon will launch an attack against the nearest target available. The demon powering Demonsoul is a low intelligence creature, bent only on destruction.