A blade that cannot — must not — be touched. A blade that does not exist.
Sheathed, when at rest, in sun-tempered golden-sheened glass or something very much like it, hilted in nothing — for it seems to hover just above its gold-flecked glassy hilt of spiraling, twisted bars — Null is an emptiness where a slender single-edged shortsword should be, a spot of endless, bottomless, eternal blackness upon the world.
It must not be touched.
* Null ignores armour, defensive magics, and essentially everything but the ability to get out of the way of its touch. That touch deals maximum damage and, if applicable, will sever a limb or other suitable chunk clean off its victim 90% of the time.
Yes, one could carve through a door or wall or whatever with Null; but doing so runs the risk of fumbling, even a little, and injuring oneself with the thing.
Beware. Null cares not about its bearer.
* A tear in the fabric of existence, bound into blade-shape and barely anchored to sorcerously infused glass? One would be forgiven for assuming this was some mad wizard’s folly.
Alas, Null is no such thing — it was screamed into existence by the final rage-fueled grief of the lone survivor of the Red Iron March against the drakkalv kingdom of Riviek, and the first use of its non-existence annihilated that survivor’s sundered heart by their own hand.