Niðavellir is a realm from Book V of Fire Emblem Heroes. It is the land of the dvergar, a race of small folk that have unlocked the secrets of technology and magic- seiðjárn.
Long ago, the dvergar were ruled by the Jötnar of Jötunheimr. At some point, a young dvergr used his craft to build weapons which allowed dvergar to fight on equal footing with the jötnar and gain independence. That young dvergr was named king, and founded Niðavellir. Afterwards, said king fostered a culture of inventors, leading to the creation of seiðjárn.
It has two treasures of it's own: A crown passed down by the royal family of Niðavellir which grants the strength to protect the realm, and a powerful blade named Gramr. However, because the Niðavellir army uses seiðjárn weapons, such regular swords fell in disuse, and Ótr offered Jötunheimr Gramr as a peace offering after relationships with them devolved to the point of leading to war.
Decades prior, a coup d'état toppled the kingdom of Niðavellir and the old king was killed, leading the country to fall to ruin and completely unable to muster a force large enough to invade a country. Eventually, a soldier named Fáfnir seized the throne by force and journeyed to Niðavellir Tower to complete the ascension ceremony that would make him king. Entrance to the tower required that he was of Niðavellir blood and bore the Crown of the Dvergar, and, despite possessing the crown, the door to the tower did not open for him. Fáfnir acted as if he had successfully completed the ceremony, and became the king of Niðavellir. The people welcomed his rule, ignoring the fact that he was not dvergr royalty. But the righteousness they thought they saw in him didn't last long, as he'd quickly become a tyrant, subjugating his people and invading other countries, with families separated to add bodies to the war effort, and food scarcity due to the constant warfare. Eventually, they sought to occupy Askr and secure the summoner for Niðavellir. He does so with an army of seiðjárn steam units.
Princess Reginn, who was among the first to enter Askr as part of the invasion, was swayed by the Order of Heroes and ended up joining them. She suggests that they seek out Eitri, the forest sage, to find a way to defeat Fáfnir. Eitri agrees to help them, and reveals that the Crown of the Dvergar is the source of Fáfnir's unusual strength. She says the only way they could stand a chance against Fáfnir is if they retrieve Gramr from Jötunheimr. The group runs into Princess Dagr, who challenges them to a bout of combat before agreeing to take them to Jötunheimr.
While in Jötunheimr, Kiran is captured by Ótr and brought to Eitri, who requires the summoner's soul to create Járngreipr, a weapon capable of destroying gates to other worlds. The Order of Heroes and the Jötunheimr princesses follow in quick pursuit thanks to Reginn's compass, which allows her to locate Ótr. Ótr fails to defend Eitri's sanctum, resulting in Eitri summoning incomplete versions of Heroes with a replica of Breidablik in defense, which show up without souls. Ótr and Eitri flee with Kiran, but the Order and the Jötunheimr princesses catch up and rescue Kiran, Gramr, and Breidablik, forcing Eitri and Ótr to retreat. When Peony shows up and warns the Order that Fáfnir has launched the next phase of his invasion, the Order rushes back to Askr.
During his invasion of Askr, Fáfnir was captured after attempting to get information out of Queen Henriette, and imprisoned in the dungeons. After being freed by Loki, he returned to Niðavellir. Ótr sways him into moving his sights to conquest of the Emblian Empire.
Later on, however, the capital of Niðavellir is completely devastated by Fáfnir, now turned into a mechanical dragon with Ótr at his side. Finding Gramr with him, Reginn attempts to get the blade back but Ótr refuses and reveals that Reginn is the true princess out of the three siblings and he resented her for that as his parents were killed by the royal family. Making a last stand against the Order, Ótr falls in battle for the last time where Reginn takes Gramr by force but she refuses to kill him. Utterly baffled at Reginn's kindness toward him despite his attempts to kill her, he uses the last of his strength to head toward Fáfnir believing he now has purpose. Fáfnir now completely consumed by madness, fails to recognize his brother and swiftly kills him.
- Niðavellir Tower - The tower used for royal ascension ceremonies.
- The Forest of the Sage - The forest Eitri calls home. It's filled with traps she invented to deter visitors.
Notable people from Niðavellir
- Fáfnir - The King of Niðavellir who rose from his station as a lowly soldier but remembers nothing of his past.
- Ótr - The Stepbrother of Niðavellir's king, Fáfnir who worships him and fully supports his ambitions of conquest.
- Reginn - The Stepsister of Niðavellir's king who chooses to work together with Askr to stop her suddenly changing brother.
- Eitri - The forest sage. She is the one who was summoning heroes from other world, until five years prior to the events of Book V.
Niðavellir, also called Myrkheim, is the home of the dwarves in Norse cosmology.