The unnamed fire sword was a fire sword sought by Lord Hater before "The Prisoner" and also the only thing that was not destroyed by Wander during his flashback.
In the flashback, Hater was holding the sword while an aura of fire was formed in him. He said "I have the power-" right before Wander threw some water at him and the sword.
Despite not having been destroyed, Hater probably threw it away since It's power must have come from the fire, which was doused by Wander who, as already stated, threw some water at the sword and Hater.
The sword was originally pure white while held by Hater. It's appearence was fully shown after it was doused with water: The sword has a dark grey bat-like hilt with a purple orb at the pommel and a silver blade with a purple orb.