Brün is the leader of the Dísir, Bor's valkyrior. At one point in the past, Brün started a rebellion against Bor and her valkyrior started feeding on other Asgardian Gods. When Bor discovered what the Disir were up to, he cast them out of all the realms, to exist in the spaces in spirit alone. They were cursed them to remain forever hungry and feed only on the spirits of Asgardian Gods, for they would only be in Asgard or Hel.
Major Story Arcs
Siege of Asgard
Ages later, Loki had surmised a plan with Norman Osborn, the director of Hammer and leader of the Dark Avengers to invade Asgard. Before the Siege on Asgard, Loki summoned them in Latveria. He managed to get Brun and her Disir to submit to him. He made a deal with Hela, who no longer had her own realm that he would give her a realm if she would spare his soul. After she agreed, Loki showed Mephisto the power of the Disir and gave them to the dark lord in exchange for giving Hela a portion of his realm. The deal was made, Mephisto gave a portion of his kingdom for Hela to govern for a thousand and one years in exchange for the Disir's service to Mephisto for a hundred and one days. During the Siege, Brun led the Disir to Asgard and attempted to devour the souls of the fallen Asgardians but Hela had sent Danielle Moonstar, a former mutant who had owed her a favor to guide the fallen Asgardians to Hela's realm as a Valkyrie.
Brun and her fellow Disir have become warriors of Mephisto and do his bidding. Mephisto had grown a fondness for Brun, who plotted to give herself and all of her fellow Disir to him if he would allow them to invade Valhalla and feed on the fallen Asgardians. When Mephisto agreed to let them invade Valhalla, Brun led her forces into Hel's realm and attacked the fallen gods and even Hela herself.
The Disir invasion of Hela's domain was unsuccessful and they were forced to retreat back to Mephisto, where he rules them harshly. But once Hela and Mephisto learned of The Serpent's plan to take over all the underworld Brun, Hlokk, Kara, and Gondul, along with Leah and Tyr were put under the charge of a reborn Loki. Loki promises Brun and her sister there freedom as long as they obeyed him. There first job was to kill the Hel Wolf so that Loki may ride it soul to Limbo.
Later when Loki's Magic Secret Action Squad attacks the Dark Asgard, Brun leads the charge with her sisters. During the attack Brun reveals to Kara that she has feeling for Tyr and before they leave she saves Tyr from being blind sided, Tyr never knows this.
After successfully defeating The Serpent, Loki frees the Disir from the Oath they made with him, but that reverts their ownership back to Mephisto. This makes most of the Disir panic but Brun excepts her fate, saying forever makes liars of us all. She is later seen being used a paper for Mephisto to write a thank you to Loki.
Trapped in Mephisto's Hell the Disir are used as Mephisto's play things, until a mysterious final portion is revealed and Brun commands her sister, come. They next appear in San Francisco in the home of Sigurd but before they can attack him the New X-Men, Hela, Tyr, Leah, Loki, Thor, and the Warriors Three show up. The Disir are about to fight but Sigurd shows up once again this time with a scroll and all Asgardians disappear leaving the New X-Men to wonder what just happened.
It turns out that Sigurd's scroll made all Asgardians in the nearby area forget who they were and bent reality to give them mortal lives and memories. Brun, keep her name and now possessed a tattoo over her eye. She now belonged to a support group for disordered eaters in recovery, Dis.I.R. She thought like the rest of the Disir she couldn't eat anything but one her way home she ate a stray cat and learned she could eat again.
Brun brought this revalation back to her sister who, once they ate normal food, learned they were the Disir once again. By this time Loki and Hela remembered who they were and along with Moonstar fought back the Disir. Then it was revealed the real reason the Disir are cursed by Bor, wasn't because theate human flesh. it was because Brun fell in love with Sigurd and abbandoned her post and was wlling to leave Bor for Sigurd.
Bor cursed her and her sisters until the day Brun killed Sigurd or he married her. It was years after the curse that Brun realized that Sigurd was not coming back for her, and she planned her revenge. Now back in the present Loki and Moonstar devised a plan. Bor was brought back from Hel to preside over the marriage of Brun and Sigurd, but Moonstar objected, and cut Bor.
The Disir went into a frenzy and attacked Bor, his only escape was to lift the curse. Brun then agreed to be Hela's personal guard and went back with her to Hel.