Sveinn Svarthæð (スヴェイン・スヴァルトヘイズ) is the king of the country of Svarthæð. It was he who unified the Nótt Álfur in a single country after many years of struggle. He is the father of Rúrik, Helga, Sigurð and Críe.
He was completely left out from the anime.
Sveinn is a tall, imposing man. Like all Nótt Álfur, he has brown skin and pointy ears. His hair appears to be gray and he has a distinguished beard with a serious expression in his eyes most of the time.
When he was young, he used to be a slave until he killed his former master and escaped. With nowhere to go and no means to have a decent life, he appeared to be destined to become another lost Nótt Álfur in the sad history of their race in Álfheimr. But shortly after escaping, as he was considering a life of crime, Sveinn met Queen Ísalind, Mercelída's mother and predecessor. Captivated by her beautiful eyes, he listened to the advice she gave him advice on what path he should follow to truly extract his vengeance on the system that caused his race to be enslaved and how he should learn to be as cool-headed as he was hot-headed. She also gave him his deserved money that was taken from his enslaver as compensation, since Ísalind's Kingdom had ordered to free all slaves and Sveinn's enslaver refused to comply. As he was contemplating the means to start his venture, Ísalind also checked his family jewels to make him aware that to accomplish his goals he will need descendants.
It appears that the mother of Rúrik, Helga and Sigurð is long deceased by the time the story begins. At some point, he met Críe's mother who was an Álfur, which resulted in Críe's birth. Due to her heritage, Críe was born as a mottled child (まだら子, madarako), so both her and her mother decided to live their lives in hiding due to the taboo of mottled children among Álfur and Nótt Álfur while Sveinn gave them everything they needed.
At the start of the story, Sveinn finally brings peace to the Nótt Álfur after 20 years of conflict among them. Achieving peace among the several tribes of Nótt Álfur and establishing the country Svarthæð by unifying all tribes under his rule, he sets up to establish friendly relationships with Ygvarland, making Helga the representative of the country of Svarthæð in Ygvarland and enrolling his Sigurð in a school in the country with Mecelída's help.
Later in the story, Sveinn is poisoned by Rúrik as part of Rúrik's plan to assume control of the country, but Sveinn, having knowledge of Rúrik's dark character, was prepared and left countermeasures in the form of making Sigurð his successor prior to Rúrik's action.
Miraculously surviving the attempt on his life, he whishes that Sigurð continues as the leader of the Kingdom, but Sigurð quits as soon as he finds out that his father survived, despite his father's wishes to leave him as the new king.
It appears Sveinn is incredible durable as he outlived both mothers of his children and survived Rúrik's attempt on his life.
Sveinn has a serious personality in appearance has he is most concerned with bringing peace to his race. He loves all his children. He is stern with Sigurð as he has high hopes that he becomes his successor as he is wary of his Rúrik despite appearing more qualified than Sigurð. He doesn't know how to deal with Helga's father complex and fully supports Críe. When the occasion arises, he bonds with Sigurð very easily as they both appear to share a similar vision of life. He Críe and his mother when they lived their lives in hiding due to Críe's heritage.
He is a wise king, an skilled soldier and an excellent tactician. He foresaw his son Rúrik's treason and planned ahead. Instead of using force, he prefers a more accommodating approach and would rather negotiate with his former enemies than try to conquer them by force. He deeply admires Ygvarland and the succubi's rule on the country. Sveinn in particular holds Ísalind in high respect, the former queen that showed him the path to change his destiny.