Fairemere Blade, Variant (5e Equipment)
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Weapon (longsword), legendary (requires attunement by killing a humanoid with the blade on you)
A blade containing the humanoid souls that it has slain. In order to use the true power and be bonded to this weapon, you must use it to take the life of a humanoid, trapping it's soul within the steel. This is the equivalent of attunement. You have a +1 bonus to attack rolls with this magic weapon. Once attuned to, you gain disadvantage with all other weapons apart from Fairemere.
Soul Absorb. Whenever you kill a humanoid or whenever a humanoid dies while within 10 feet of you, their soul is sucked into the blade.
Trapped Souls. For every humanoid soul consumed by the blade, this weapon deals an additional 1d4 necrotic damage on its damage rolls. This weapon may absorb 6 souls, but at dusk of every day, the weapon loses a soul.
Power of the Soul As Fairemere must feast on souls to gain power, if a day passes without it taking the souls of a humanoid, it deals xd6 damage to the wielder, where x is the number of the days passed without consuming a humanoid soul.
Cursed. The only way to put the souls trapped inside Fairemere to be put to rest and end attunement, is if the holder slays themselves with the blade. Only then, can the souls be released and put to rest in whatever higher plane they believe in. Once this happens, Fairemere soul count resets to 0, and waits to be picked up by its next slave.