Sumarbrander

''This article is about the sword. You may be looking for the book.'' Sumarbrander or Sword of Summer is Magnus Chase's sword, formerly owned by his father, Frey. It is said to be the sharpest sword in the Nine Worlds. After becoming its master, Magnus decided to rename it Jack.

History
Sumarbrander was a magical sword, originally owned by the god Frey. Frey fell in love with a frost giant, Gerd, who he was not allowed to marry. Frey ended up trading his sword to Skírnir to kidnap Gerd and bring her to him. Sumarbrander ended up being betrayed by its original master, although it continued to obey Skirnir.

The Sword of Summer
Magnus retrieves the sword from the bottom of the sea before Surt attacks him. Magnus dispels Surt with the sword. Magnus looses the sword at the bottom of the ocean after dying in the human world. After retrieving the sword by bargaining with the sea goddess, Ran it turns into a necklace.

When visiting Freya, Magnus learns about Sumarbrander's past with its original owner Frey. Freya tells Magnus that the sword has "special abilities" that he will need to learn to master.

While running away from Junior, Magnus pulls out Sumarbrander, who ends up having the ability to talk.

Abilities
Jack is a sentient blade; it has the ability to speak and understand human language (although, as it says, it can't speak Alf Sign Language). When not used by Magnus, Jack takes the form of a runestone pendant with the Fehu rune - the symbol of Frey.

Jack is also very effective against the Jotunn, and it can fight them on its own. It is also the only thing capable of cutting through Gleipnir - enchanted extremely durable rope that used to bind Fenris Wolf.

Whenever the holder of the blade retrieves it after an action, they receive the consequences of the action that the sword has preformed.

Etymology
The sword's Old Norse name means "Summer sword".

Trivia

 * In the mythology, Frey's sword is never named.
 * Sumarbrander is destined to become Surt's possession and kill Frey during Ragnarök.
 * When discussing what form should Jack become when not a sword, Magnus suggests a pen. Jack comments that a pen sword is 'the stupidest thing he's ever heard'.
 * This is a nod at Percy Jackson's sword, Riptide, which becomes a pen when "capped".