Balmung

is the Noble Phantasm of Siegfried. It is a two-handed, golden greatsword with a blue jewel embedded in the hilt that boasts a magnificence and enormity that makes it seem as if it was created by inhuman hands.
He received Balmung from the family. The Nibelungs, a tribe which lived in an underground country, requested that Siegfried fairly and impartially divide up and distribute their treasure, and he accepted the request. Balmung was planned to be given to him as payment for this. However, two kings felt that the allocation of treasure was done unfairly and fought Siegfried, but he killed them in return. The remaining treasure which no longer had an owner became Siegfried’s, and Balmung also became his weapon. He wielded Balmung in every battle after that. It is also said that he won in the battle against Fafnir thanks to Balmung. After Siegfried's death his wife Kriemhild wielded Balmung as part of her revenge, using it to kill Hagen, the man who killed Siegfried.Fate/Grand Order material I - Siegfried, p.052-061, translated by Mazyrian & GundamFSN at Beast's Lair.
It is the holy sword of the Nibelungs, used to slay the dragon, Fafnir. It is a cursed holy blade possessing the attributes of Gram, the demonic blade of its origin, so it will change attributes between holy sword and demonic sword depending on who wields it. Having accomplished the feat of dragon slaying, those with the blood of dragons will take additional damage from it. Perhaps because it was owned by a king, it specializes in fighting against armies, shooting off a semi-circular slash wave.
Upon chanting "—O sword, Let thee be filled", he holds it above his head, and it begins to glow with an orange light. The jewel stores and preserves magical energy, True Ether from the Age of Gods, and releasing it causes it to emanate a twilight aura. The twilight swells around the sword and is released as a flash of light, a surging wave with the simple purpose of destruction. Compared to the straight line released by Clarent Blood Arthur, it releases a wave of twilight in a semicircle that is centered around him.
It has an extremely fast activation rate for an Anti-Army Noble Phantasm, but in a comparison of speed, Siegfried when he was alive was the fastest in activating it, with Sieg being the next fastest and the Servant Siegfried being the slowest out of them. Sieg possesses Galvanism, which the Servant Siegfried does not have, and can draw out the needed magical energy all at once when activating the Noble Phantasm. The living Siegfried, on the other hand, had his inborn disposition combined with the transformation of his heart into a Magic Core due to being bathed in and drinking a dragon's blood, so he could draw forth magical energy and fire the slash wave even faster than Sieg. Unfortunately, the moment he was summoned as the Servant Saber, that special characteristic of his was highly degraded.
Boosting Balmung with a Command Spell transforms it into an Anti-Fortress Noble Phantasm, allowing Siegfried to achieve the True Ether full release of the sword. In this form, it is powerful enough to destroy Fafnir with a single shot, despite being equally matched before.
When Sieg battles Karna, he is able to use Balmung together with Galvanism to great effect and is able to activate Balmung consecutively. After witnessing two back-to-back attacks on the level of Brahmastra Kundala, the Lancer-class Servant decides that there is only one way to win and uses Vasavi Shakti. Balmung would have been penetrated in only two seconds, but Sieg uses a command spell to boost it, allowing it to reach an equal footing with Vasavi Shakti. It becomes a battle of will from this point on, but since Sieg's opponent was Karna, who was famous for his indomitable will, Vasavi Shakti was able to break through Balmung.Fate/Apocrypha Volume 5
==Balmung Kriemhild==
 is the Noble Phantasm of Kriemhild when summoned as a Berserker in Fate/Grand Order.
Balmung changes between being a holy sword or a demonic sword depending on who wields it. An evil slash that extracts the elements of Balmung as a cursed blade. It’s a cursed sword that can hurt even those that wield it and doesn’t protect them, but it is incredibly effective when it comes to killing its target.Fate/Grand Order - Kriemhild Profile - Translated by Lapithae 
Kriemhild took Balmung and beheaded Hagen, but was killed shortly after by a man who was outraged by her acts.
…There’s no remaining focus, just slaughtering the foe in front of you is all you need.
==References==
vi:
Category:Noble Phantasms
Category:Anti-Army Noble Phantasms
Category:A+ rank Noble Phantasms
Category:EX rank Noble Phantasms
Category:Swords
Category:Noble Phantasms introduced in Fate/Apocrypha
Category:Anti-Fortress Noble Phantasms
Category:Dragon Slayer Noble Phantasms
Category:Anti-Unit Noble Phantasms
Category:Noble Phantasms of Siegfried