Sif is mentioned twice in The Sword of Summer. First, her name is seen tattooed on her husband Thor's arm. Thor later references the time Loki stole her golden hair. Magnus mentions that she looks like a dryad spirit that his cousin Annabeth told him about.
Sif appears to Magnus and his friends when they are being chased by the mountain giants. She saves them from being killed and brings them to Bilskinir. She gifts Hearthstone with a leather pouch of runes made from a rowan tree, but warns him that one rune is missing. She then sends them down to her husband, Thor. Then she gives then guest rooms in the upper levels of Bright Crack.
Sif once had beautiful long golden colored hair, before Loki cut it off and was replaced it with real gold hair. When she appears to Magnus Chase and his friends, she is wearing an orange-red dress clasped at her shoulder with a silver and green brooch. She has fine elfish features and had long hair of red gold which is described as rich, warm, and lustrous.
She presumably possesses the standard abilities of a goddess
- Geokinesis: As the Goddess of the Earth, Sif has divine authority and absolute control of the earth.
- Chlorokinesis: As the Goddess of Grain and Harvest, Sif could grant fertility to the earth, allowing plants to grow where they could not grow before, and even aided in the growth of plants simply by being near them.
- Sif was well known for her golden hair.
- Her Greco-Roman equivalents would be Demeter/Ceres and Gaea/Terra.
- Sif Mons, a volcano on the planet Venus, is named after her.
- According to Sam the fairy tale Rapunzel originated from the golden hair of sif.