I don't know if I should post this here, but it does go with this idea.
Mugen no Hakai(Endless Destruction)
Weapon(katana), legendary(attuneable*)
A weapon cursed upon creation, the Mugen no Hakai is a dark weapon for an evil purpose. Normally, this sword grants a +1 bonus to attack and damage rolls. It also has these additional properties:
Hunger - This sword exudes a hunger and will to draw blood. Usually an accidental discovery upon a battlefield, the sword becomes stronger when it has tasted fresh blood. This may be visible by three runes inscribed upon the blade that glow red, revealing the words "Blood Hunt".
Hunger Table: Unattuned and Unsatisfied +1 Unattuned and Satisfied/Attuned and Unsatisfied +2 Attuned and Satisfied +3
*Attuneable - When this sword is unattuned its curse behaves as a Sword of Vengeance without the possessive qualities: Whenever you take damage in combat you must succeed on a Wisdom saving throw(DC 15) or you will be compelled to attack the creature that attacked you.
Taste for Blood - To attune this weapon, the soul of the blade calls for blood. The sword attunes to a wielder that has proven itself by spilling blood in combat(using this sword). Then, the blade must also taste the blood of its wielder, granting attunement.
Sentience - The Mugen no Hakai is a sentient weapon that communicates through emotion and will. It has a Neutral Evil alignment though this has no affect on attunement. Its wisdom and charisma are on par, with intelligence as the weakest ability score. It has hearing, as well as normal vision up to 30 ft., with Taste as a unique ability(as far as I know).
Conflict Table: Hunger Level(Days to Hunger) - If the Mugen no Hakai has not tasted blood for an excess of time, it may begin thirsting and acting erratically(may attempt to strike another creature). This represents how hungry the sword may be after a battle, and how many days until it begins to grow hungry again.
Unsatisfied(1), Appeased(3), Sated(5), Satisfied(7)
One way to keep the sword in check could be by drawing a small amount of blood, and "feeding" the blade. As with the Sword of Vengeance this could be as little as a drop of blood or as much as the DM wants. One example would be applying a streak of blood to the blade daily to appease the spirit within.