Stormourne

Runeblade greatsword, with a blade at least five feet long from the hilt. The hilt itself is embedded with a large spherical ruby that often looks like an eye. A mysterious blade potent with formidable power that cleaves the soul as it cleaves flesh. The blade is made entirely from an unearthly, vaguely flesh-like black metal, and is etched with mysterious runes. The blade is often wreathed in black light and dark fire, and it screams in battle. Any being slain with Stormbringer will have his or her soul leeched out of them.

The sword is alive and self-aware. The sword can be quite vocal, screaming, grumbling, howling, murmuring, moaning, and even singing at times. It is capable of slaying even gods.

It has the following additional properties.

Devour Soul. Whenever a wielder uses it to down a creature, the sword slays the creature and devours its soul, unless it is a construct or an undead. A creature whose soul has been devoured by Stormourne can be restored to life only by a Wish spell.

When it devours a soul, Stormurne grants the wielder temporary health equal to the slain creature's health maximum. This temporary health boost fade after 24 hours. As long as these temporary hit points last and the wielder keeps Stormourne in hand, they have advantage on attack rolls, saving throws, and ability checks.

If the wielder hits an undead with this weapon, you take 1d10 necrotic damage and the target regains 1d10 hit points. If this necrotic damage reduces you to 0 hit points, Stormourne devours the wielders soul instead.

Soul Hunter. While being wielded. The wielder is aware of the presence of Tiny or larger creatures within 60 feet of them that aren't constructs or undead. Wielder also can't be charmed or frightened.

Stormourne can cast the Haste spell on the wielder once per day. It decides when to cast the spell and maintains concentration on it so that they don't have to.

Sentience. Stormourne is a sentient chaotic neutral weapon with an Intelligence of 17, a Wisdom of 10, and a Charisma of 19. It has hearing and darkvision out to a range of 120 feet.

The weapon can speak, read, and understand Common, and can communicate with its wielder telepathically. Its voice is deep and echoing. While you are attuned to it, Stormourne also understands every language you know.

Personality. Stormourne speaks with an imperious tone, as though accustomed to being obeyed. The sword's purpose is to consume souls. It doesn't care whose souls it eats, including the wielder's. The sword believes that all matter and energy sprang from a void of negative energy and will one day return to it. Stormourne is meant to hurry that process along.

Stormourne’s hunger for souls must be regularly fed. If the sword goes three days or more without consuming a soul, a conflict between it and its wielder occurs at the next sunset.