Kuroi ha

A foreign-made weapon wielded by the royal army of the Scarlet Castle. When the intricate, rippled engraving that spans the Kuroi ha's blade is imbrued with blood, the sword sings in scarlet hues. However, the rite eats away at the wielder's very essence.
These weapons are bow highly coveted by hidden cults or collectors of the strange. The High Church of Pelor has banned these weapons and sentences all who use them openly to death or capture for interrogation at the rummored Onyx Stockade.

Exotic Weapon. This finely made blade is magical and gains a +2 to hit and damage rolls. It is so sharp and well balanced that this blade critical hits on die rolls of 18-20's.
Scarlet Hues. You can take an action to sweep the blade across your gut. Doing so spills out a large splat of the attuned's blood onto the blade, and the attuned takes 12 nectoric damage. Afterwards the blade begins to sing and drips a viscous black material onto the ground. When in this state the Kuroi ha deals necrotic damage instead of slashing, and in addition it uses the attuned's spell casting ability for it's to hit and damage rolls. If the attuned does not have a spell casting modifier it can be either choice Dexterity or Strength + Proficiency modifier. This rite last for 1 minute, and can be stopped early if the blade is dropped or as a bonus action the blade is wiped clean by sheathing it.
Scarlet Rights. If you score a critical hit or kill a creature with the Kuroi ha then you regain 1d10+5 hit points back. If you manage to do both with one swing then you regain 2d10+20 hit points
Cursed Item

This sword is cursed and possessed by a vengeful spirit. Becoming attuned to it extends the curse to you. As long as you remain cursed you are unwilling to part with the sword, keeping it on your person at all times, and will stop at nothing to get it back. While attuned to this weapon, you have disadvantage on attack rolls made with weapons other than this one.

Item type

Weapon, Melee

Rarity

Very Rare, Requires attunement