Nidavellir was basically a big forge where precious metals and enchanted meterials from all around the Universe was used to create and Enchant powerful weapons. They had stock of many kind of minerals and metals. Since Uru was the best of the metals they had with highest energy channelling rate who was durable enough to handle the pressure of infinity stones, they decided to use it to craft Eir's sword.
Eir was hoping to get something even better as in original story the hammer forged from Uru easily got squeezed and destroyed by Hela, her older sister. Not to mention that infinity gauntlet basically melted after only one use of stones full power. So She inquired Eitri if he had any material even stronger than Uru. She even said that she would find the material if he tell her what to find.
Eitri after hearing that took Eir to an underground chamber. In that chamber, all kinds of metal were kept from all around the universe. Eir even saw a chunk of vibrenium there. They pass the room and stood in front of an empty wall.
Eitri said "Princess, there is a legend among the old dwarves. Legend of a God named Knull also known as the God of symbiotes. It was said that in his hatred towards Universe, he created a sword known as All-black Necrosword from the living abyss that existed before the creation. It's a weapon said to be capable of killing any life form. You know the head of the celestial that's known as the place 'Knowwhere' now, it's said that it was decapitated by Knull using Necrosword. But in that fight a small piece of that sword actually fell off and retrieved by someone later. As a unique material, it was sold to many collectors and after travelling from place to place, we finally got our hands on this." as he said this, a door in the wall appeared and opened.
Soon everything around them was engulfed in darkness and an uneasy feeling rose in air. Eitri led the way and soon they were standing in front of a glass looking box. Inside there was a tiny peace of metal of fingernale size. But it was the source of all this creepy feeling in the air.
"As you can see, we only have a tiny amount of this so we couldn't use it before. But now with Reality stone maybe we could produce more of this. I'm not sure of this as it's said to be made of something that existed before creation but we should give it a try." Said Eitri.
Eir couldn't help but feel exited from finding all this. Who could have thought that that shity weapon shown in 'love and thunder' as necrosword was actually this powerful. Maybe it lost all it's power after thousands of years and wasn't in it's best shape in the movie.
All and all she was excited giving this a shot too. As Eitri was more skilled in knowledge of metals, she left Reality stone in his hands so he could try and produce the material used in Necrosword. It would take some trial and error but she was happy that she was getting a chance to have the best.
Now that all that done, she didn't have anything better to do so she decided to learn the basic of forging and Enchantments. But soon she gave up because the weapon they were forging weren't on par with the weapon she was hoping. But she understood that Weapon's like Mijolnir or Stormbeaker were the peak of what they made and it wouldn't be good if those kind of weapons were Mass produced as that would just bring mass destruction.
So after thinking for a bit she give the remaining Dwarves the commission to modify and enhance her ship Starblade.
The dwarves were first reluctant to work on a Spaceship but when they saw the spaceship made like a sword, they somewhat agreed to work on it.
After about a week, Eitri informed her that it was actually possible to produce more of the material which Necrosword was made of.
Now all that was left was to design the blueprint of the sword and create the wonder of the universe.
Eir could only wait in eagerness. She wished she had the time stone so she could fast forward time and get the sword as soon as possible but she have to endure it like any other person.