The Salamander Dagger is one of the magical items bestowed by Flora and Schierke to Guts and his team to help Schierke in her fight against the Troll raiding Enoch Village, along with Casca's and Farnese's Silver Surcoat and Silver Dagger, Serpico's Sylph Sword and Sylph Cloak and the refused Axe of the Gnomes
As Flora's magical weapons were not intended to be used by children, Schierke had not a suitable sword for Isidro, and instead offered him the Salamander Dagger. At first frowned upon by Isidro, it was quickly accepted upon discovering its magical powers: forged in molten lava, and possessed by fire spirits, it unleashes a burning power, hot enough to melt steel and strong enough to combust a human-sized enemy whenever it strikes a successful blow.
At first meant as Isidro's primary weapon, its inherent flaws forced Isidro to make use of it as a "left hand weapon", to use in combination with his other arsenal. As the Salamander Dagger is too short to deal a blow to a taller opponent armed with a regular sword, Isidro taught himself to feint with his pirate cutlass, using both weapons in conjunction.
He also uses the fire powers of his dagger to ignite the small bombs given to him by Guts, start fires or burn through items, much like a lighter or a blowtorch.