Avengers: Endgame saw Thanos wield an immensely powerful blade, one that could actually be of Celestial origin. In Guardians of the Galaxy, Korath described Thanos as "the most powerful being in the universe." While he was clearly exaggerating a little, in Avengers: Infinity War and Avengers: Endgame Thanos proved that he wasn't far wrong. The Mad Titan effortlessly beat down the Hulk without even needing an Infinity Stone, and in Avengers: Endgame proved more than a match for the combined might of Iron Man, Thor, and Captain America. Only two Marvel heroes - Scarlet Witch and Captain Marvel - seemed able to threaten him.
In part that's because Thanos is a true warrior, and he wears armor and wields weapons that are perfectly suited to his fighting style. Thanos is already a physical powerhouse, but with that armor on he can take lightning bolts from Thor without seeming to be harmed at all. The sword is a match to that in power. Designed as a melee weapon, Thanos uses its broad blade to block attacks; the sword's length means he can spin it round in unexpected attacks, slicing his enemies down with effortless ease.
In truth, though, Thanos' Avengers: Endgame sword is something of a mystery. It's clearly incredibly powerful, possibly beyond any other single weapon seen in the MCU to date, so where on Terra does it come from?
Thanos' Endgame Sword Was Way Too Powerful
The sheer power of Thanos' sword in Avengers: Endgame is best illustrated by comparing it to Thor's two weapons, Mjolnir and Stormbreaker, both of which were forged on Nidavellir. "That place is a legend," Rocket declared in delight when Thor mentioned Nidavellir. "They make the most powerful, horrific weapons to ever torment the universe." What's more, as impressive as the Nidavellir-forged Mjolnir has long been, Stormbreaker was supposed to be one of the most powerful weapons the Dwarves of Nidavellir had ever created. According to Eitri, it was designed to be a King's weapon, the greatest in all of Asgard. It could summon the Bifrost, which meant it potentially had the power to destroy entire planets, and it proved able to resist a beam projected from all six Infinity Stones at once. And yet Thanos' sword was superior to Mjolnir, and at least equal to Stormbreaker; he was able to block Thor's strikes with his weapon and knock Stormbreaker aside with contemptuous ease
Perhaps even more confounding, he could use the blade to hack Captain America's vibranium shield to pieces - a shield that Mjolnir couldn't break or buckle. Frankly, this is easily the single most impressive and potent melee weapon in the MCU to date, more formidable than anything the Dwarves of Nidavellir have ever forged. Thanos must have gotten it from somewhere else.
Thanos' Origins Tie To The Eternals - And The Celestials
Although the MCU has switched Thanos' character and motivations up a little from the source, his origin appears to be pretty much comic book accurate. In the comics, Thanos' homeworld of Titan was a colony of the Eternals, an evolutionary offshoot of humanity created by a powerful race known as the Celestials. The Eternals have superhuman abilities to equal (or even best) any Asgardian, and their technology is millennia ahead of any other civilization's, inspired by their Celestial creators.
The MCU's Thanos was obsessed with the Infinity Stones, and assuming a similar Eternal origin, it's likely that this obsession also meant he had focused on the Celestials as well. As revealed in Guardians of the Galaxy, the Celestials were the earliest known masters of the Infinity Stones, using them to mete out judgment on entire worlds. Indeed, it's distinctly possible the Celestials were the ones who forged these six singularities down into Stones to begin with.
Did The Celestials Make Thanos' Endgame Sword?
The MCU has subtly redesigned the Celestials, whose last survivor Ego was introduced in Guardians of the Galaxy Vol. 2. In the MCU, the Celestials are essentially energy beings who could manipulate matter on a molecular level, creating anything they wish. While many of their forms were giant-sized - the space station Knowhere is the severed head of a Celestial - there's no reason a Celestial couldn't make an ordinary-sized body. And it could easily create a sword beyond anything even the Dwarves of Nidavellir could envision.
All this raises the possibility that Thanos' sword is of Celestial origin, a weapon designed by the Eternals' creators themselves. Thanos' quest for the Infinity Stones would logically lead him to worlds where the Celestials had historically been active, and perhaps even to the planets where they had lived and died. If anyone is going to retrieve Celestial artifacts, it's Thanos; and he would no doubt be fascinated by a Celestial weapon, training himself to master it.
Frankly, there's little to work against this theory barring an explicit disproof; it makes a lot more sense than pretty much any other explanation for the shield-breaking, Stormbreaker-blocking weapon's existence.
What Happened To Thanos' Sword After 2014?
As impressive as Thanos' sword may be, it's interesting to note that it was only used by the Thanos of 2014. In Avengers: Infinity War, Thanos didn't use either the sword or his suit of armor, and according to Marvel that was a conscious choice on his part. "Clothing Thanos was a fun challenge because we needed to have essentially a wardrobe of ideas of what he may begin to wear as he gets more and more powerful thanks to collecting more of the Infinity Stones and not really even needing armor anymore," concept artist Wesley Burt explained in The Art of Avengers: Infinity War. "He would then begin to become more of this philosopher sort of personality with clothing reflecting that."
By the same logic, then, Thanos wouldn't see the need to carry his sword either. Avengers: Infinity War begins with the Mad Titan already in possession of the Power Stone, which he used to take down an Asgardian refugee vessel; he rightly didn't imagine a bunch of civilians to be much of a threat. Once he'd acquired the Space Stone, he was already a third of the way to collecting all the Infinity Stones, so presumably didn't feel he needed another weapon. And he was right: although it was a close thing, he did accomplish his insane goal of erasing half the life in the universe with a snap of his fingers.
What this means for the future of the MCU is that Thanos' Avengers: Endgame sword is still out there. He turned his armor into a scarecrow, but the dual blade's location remains a mystery; it's presumably adrift in space on the Sanctuary II, ready for someone else to claim.
