WARNING: The following contains spoilers for King Thor #2, by Jason Aaron and Esad Ribic, available now.
The Necrosword already had a deadly reputation for its near-omnipotent power, and it only keeps getting stronger. In Marvel's King Thor #2, Gorr evolved the blade into its final form, a massive weapon that dwarfs its wielder and target. And it's in that form it destroys an entire planet in one fell swoop.
The sword has a long history that stretches back into the cosmic mythos of the Marvel Universe, and stands at a nexus between two seemingly unrelated properties: Thor and Venom. While it was introduced by writer Jason Aaron and artist Esad Ribic in their earlier Thor: God of Thunder series, its backstory is fleshed out in Venom, by Donny Cates and Ryan Stegman. The weapon has become increeasingly prominent, and it's easy to see why, given how important it is.
Created by the god the symbiotes, Knull -- the same god Carnage seeks to release in Absolute Carnage -- the Necrosword was created in the fires of a Celestial's death. It furthered its reputation for murdering such divine entities in the hands of Gorr the God Butcher, who sought to eradicate all godly beings from reality, one death at a time. When his plans were foiled, the weapon passed to Thor, followed by Galactus, and then Ego the Living Planet before finally falling into the hands of Loki.
It was in his possession that the Necrosword devastated much of the known universe prior to the future setting of King Thor. However, it turns out that Gorr's business with the blade was not over. Before Loki could release a final coup de grace on his brother, Gorr revealed that a piece of him survived in the blade, and he emerged to reclaim it. Entering into battle with Thor himself, Gorr revealed the Necrosword has a final form.
While already the weapon already bears the name of the Necrosword and the All-Black, Gorr dubs its truest form, the Annihilablade, the Planet Cleaver, and the Final Doom of the Gods, as it swells in size. Like a giant starship with a blade on either end, the Annihilablade is commanded by Gorr to rip through a planet. King Thor's only hope for fighting it is to wield massive supernovas like weapons, but the sword cuts through the first one with no apparent problem.
There seems to be no beating it. After the cosmic battle, Thor and Loki join forces in hope of being able to stop the newly dubbed "God of God Butchers," but to little avail. Gorr ultimately consumes the two of them in utter darkness after critically injuring the pair, and by the issue's end there appears little hope for a comeback.
Despite the climactic nature of the fight, however, it occurs at only Issue 2, and it's safe to say that there is some glimmer of hope for the brothers' return. King Thor's granddaughters still roam the cosmos in search of a way to restore the spark of life to the stars, and the primordial remains of humanity cling to the prayers for their god despite the apocalypse around them. Still, given the sheer power of the Necrosword, it's difficult to imagine anything that could possibly beat it.