I’ve been giving some thought to a 5e magic item based on the sword from Legacy of Kain: Soul Reaver, based mostly on the idea of a magic item that’s powered by psionic forces in some way rather than a physical item.
Here’s what I’ve come up with so far:
Weapon (varies), rare (requires attunement)
A curious ball of floating colourful energy that, once attuned to, becomes a loop of filigree energy around the wrist of the user. As a free action, the user may draw’ the blade and extend it to become a weapon of psychic force.
Functions as a +2 dagger, shortsword, longsword or greatsword (chosen by the DM when found), deals two dice of pyschic damage in the size usually used by the weapon – i.e. this is a +2 longsword that deals 2d8 psychic damage.
(I’m debating adding an ability that deals some form of extra damage by spending a hit die, but that’s still up in the air.)