Sif is a fierce young Asgardian warrior and the one person who truly believes in Thor, even as she refuses to flatter him. She is the first to tell the prince the hard truth, that the celebrated Einherjar let him win his matches because no one dares defeat the son of Odin, and when he challenges her over it, she bests him soundly with nothing but a barn tool. Stung by how Asgard treats her and seeking to reach her full potential, she leaves to join the Valkyries, the sisterhood of warrior women training in the branches of Yggdrasil.
Her path crosses Thor's again when his forbidden quest turns to disaster. He comes to the Valkyrie camp begging her help to get home with the Sword of Surtur, only for the pair to be seized by Brunhilde and her warriors. When Frost Giants attack the camp, Sif fights alongside the Asgardians, and Brunhilde, seeing her worth, sends her to escort Thor and the others safely home, telling her to return only when she is truly ready. She proves herself in the battle for Asgard that follows, earning at last a place among a new Einherjar on her own merit rather than any man's favor.