The Sword of Asha is an ancient relic, the weapon used by the angel Asha in her final battle against Malfegor. The sword was broken into twelve pieces, which were buried under the Twelve Trees of Valeron.
Thanks to the Order of the Skyward Eye's manipulation of the Prayer of Asha, the Sword of Asha was widely regarded little more than a myth at the time of the Conflux.
Ultimately, the rhox Mubin realized the sword was real, dug up the pieces and had it reforged. It was then given to Rafiq who managed to kill Malfegor with the weapon.