Asuramaru

Cursed Atunement. If any creature picks up this weapon while it is not attuned to another creature, it will immediately attune to that creature and cannot be unattuned by any means except the wish spell. 

Possession. This katana contains the soul of a fallen vampire turned demon named Asuramaru. Asuramaru is a sentient, neutral evil item with an Intelligence of 19, a Wisdom of 18, and a Charisma of 20. He has hearing and darkvision out to a range of 120 feet. Asuramaru can speak, read, and understand common, elvish, abyssal, and infernal. In addition, he can communicate telepathically with any character that carries or wields it. 

Like all demons, he is manipulative and uses nightmares to erode a person's constitution for the purposes of possessing them, in order to take over his host's body.

If the attuned creature falls below half their remaining hit points, Asuramaru will attempt to take control of them. The attuned creature must make a DC 18 Charisma Saving Throw. On a failed save, the wielder is charmed by the item for 1d12 hours. While charmed, the wielder must try to follow the item’s commands. If the wielder takes damage, it can repeat the Saving Throw, ending the effect on a success. Whether the attempt to control its user succeeds or fails, the item can’t use this power again until the next dawn.

Animate Object. This weapon has the statistics of a draconic shard except it cannot inhabit any other weapon and is tiny in size (The size and shape of a Katana). Asuramaru can act as a creature until he falls to 0 hit points. If Asuramaru falls to 0 hit points, he cannot act as a creature until he rejuvenates (Other abilities on this sword can still be used by the attuned creature). 

While acting as a creature, Asuramaru can shape change into a medium-sized humanoid (keeping all other statistics). While doing so, Asuramaru appears as an androgynous adolescent male with long dark purple hair that goes beyond his feet, while his bangs cover his left eye. As a demon, an entity that was once a vampire, Asuramaru has red eyes, fangs, and pointed ears. He wears a sleeveless open-back dress including a collar with gold beads covering his throat. The chest piece is black while the rest of the dress is white, and the gown splits open at his outer thighs which would free his legs for movement. The black sleeves Asuramaru wears are separated from the gown that reach his mid-upper arms and come down to his middle fingers, where each sleeve is attached to a ring. He is barefoot. On Asuramaru's head is a headband formed of two parallel golden strips that match the horns piercing through his hair from the edge of his hairline.

Artifact Properties. This weapon gains the following properties while attuned to a creature:

• This weapon gains a +3 to attack and damage rolls and deals 3d6 extra necrotic damage on a hit.
• The attuned creature gains resistance to psychic and necrotic damage.
• The attuned creature can telepathically communicate with Asuramaru regardless of whether they are on different Planes of Existence or not.
• The attuned creature and summon or dismiss the sword to a demiplane as a bonus action (Possession can still happen regardless of the Plane the sword is on). 

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Resistance: Psychic, Bonus: Magic, Resistance: Necrotic, Versatile, Sap