Haven't seen it yet, but as a Norse mythology buff, I am glad to hear Sif ends up a romantic interest. In the name of he who hung upon the tree Yggdrasil for nine days and nine nights, she is supposed to be Thor's wife. Also, she is supposed to be blonde. This isn't minor, her nickname (like Odin is the Allfather, Thor is the Thunderer, Freyja is the Lady of the Slain, ect) is Sif of Golden Hair. In a early myth her hair is described as being like sunlight flowing across gold, then Loki cuts it off as a prank, then Thor threatens him, then he makes the Sons of Ivaldi make her new hair out of literal gold, and by a bet gets dwarves to make Mjölnir (you know, the Hammer of Thor?), Gungnir (Odin's spear), Gullinbursti (Freyr's golden boar, can run across water), Draupnir (Odin's magic ring, makes 8 copies of itself every nine nights), Skidbladnir (Freyr's ship, can shrink or grow as needed, always has wind in its sails) so her being blonde is kinda important. Also she is a goddess of farming and fertility, not war.