The Sommerswerd is a holy, magical artifact with tremendous effects against the minions of Naar. It was forged by the Nuoma, a race of god-like beings, and brought to Magnamund by the Sommlending (a race of fair-skinned humans with special powers).
The Sommerswerd is a golden broadsword, but can also be wielded as a sword or short sword. Only a Kai warrior can effectively wield it. If someone else does, its power might be lost forever. Non-humans can pick up and hold the weapon, though it will damage those of evil intent.The Sommerswerd greatly increases one's combat prowess. It has the ability to absorb any magic used against its bearer and is able to slay Darklords and the undead. It increases one's Sixth Sense. It is said only a true son of Sommerlund can release the powers that lie within the blade. The Sommerswerd's powers can be contained and hidden in Korlinium. It draws its power from the sun. It is one of the few weapons, other than those created by the Nadziranim, capable of killing a Darklord.
Its supernatural powers increase the bearer's Combat Skill by 8 (prior to the application of weapon skill bonuses, of which either Short Sword, Sword, or Broadsword apply), and also increase the sensitivity of his Sixth Sense. It is doubly damaging to undead foes and absorbs hostile magic. As the weapon was created by the god Kai and is a direct representation of his power, it is one of just a few weapons capable of killing a Darklord and, as stated in The Curse of Naar, it might be able to kill Naar himself.
The Sommerswerd was created by a god-like race called the Nuoma and was sent by the God Kai with the Sommlending people to destroy the Darklords and keep the dark god Naar from taking over the world of Magnamund. Ulnar I was the first to wield it and used it to kill Archlord Vashna at the Maakongorge. Later, it was given to Durenor as a symbol of the mutual trust between the nations. In return, the Durenese gave Sommerlund the Seal of Hammerdal with a promise that the Sommerswerd would be returned on demand to the bearer of the Seal. Lone Wolf recovered the sword in the aftermath of the Massacre of the Kai and used it to destroy the Darklord Zagarna. He kept it, and has since used it to conquer his many foes.
The Sommerswerd is one of the more controversial items in the series, in that it is believed to have a negative effect on the overall difficulty of the gamebooks. Joe Dever has said that the sword's bonus made it difficult to create balanced statistics for enemies; those that would challenge someone with the weapon but not overwhelm someone without it.
Beginning in the Magnakai series, some battles become more difficult if the Sommerswerd is used. This is explained that its divine presence alerts Lone Wolf's foes, or causes them to use more powerful weapons to offset the advantages of the sword. Occasionally this has the opposite effect, and some books become more difficult to complete if wielding the Sommerswerd.
It can be noted that the actual name of the sword is likely derived from Old English “Sumorsweord”, unless it is from an elderly variant of Swedish ("sommarsvärd" in contemporary Swedish) ; in both cases the name translates in Modern English as "summer sword".