You target a creature and attempt to weaken their soul.  The targeted creature must make a Constitution Saving Throw.  On a save, this spell has no effect.

On a fail, the creature’s current Hit Points become its new Hit Point Maximum until the creature is effected by the Greater Restoration spell or similar magic.

If this spell is cast on a creature that is at 0 Hit Points and fails the Saving Throw, they die and can not be revived by anything short of a Resurrection spell or higher magic.

If the 9th level version of this spell is cast on a creature who fails the Saving Throw and is at 0 Hit Points, they can not be resurrected, not even a Wish spell can remove this effect.