Lightning is the sword of Lady Knight Alanna of Pirate's Swoop and Olau. She first found it while she was on a trip with Myles of Olau in the barony of Olau exploring ruins of the Old Ones. There the sword saved Alanna from death by using its own magic. The sword is most probably a relic of the Old Ones and Myles voices the opinion that the Gods wanted Alanna to have it.
Lightning later breaks when Alanna fights hill bandits in Tortall's Great Southern Desert. She makes several tries to repair it, but its strong inherent magic prevents her from reforging it. Instead she combines it with the crystal sword by using magic based on a Bazhir ritual.
It is described as being lighter than a broadsword, but double edged like one. The hilt was studded with gems and was topped by a crystal, which had several unbiddable magical powers.