Soul Calibur is the spirit sword created to combat Soul Edge. Algol, the king that once wielded Soul Edge and lost his son because of the demonic sword, vowed to create a holy sword from the purified shards of Soul Edge that would oppose the evil sword, being his equal in strength and opposite in intent. Algol enlisted the help of the greatest sage in the land, who used purified fragments of the cursed sword to forge Soul Calibur. After many failed attempts, the holy sword was born as Algol sacrificed himself to perform such feat. However, the sword that was created was far from good due to Algol's thirst for power in his dying moments, and it was extremely similar in nature to Soul Edge. Nonethless, the tribe that was tasked with guarding the sword slowly purified it to the point that it could be considered a holy weapon, while keeping dormant the soul that rested within the sword. The guardians lived in seclusion, passing the sword from generation to generation in secret. Whenever a warrior vowed to take on Soul Edge on his own, Soul Calibur appeared to prevent the cursed sword from causing any more damage. Soul Calibur finally appeared, in disguise, as one of the Ling-Sheng Su Temple treasures, a sword called Krita-Yuga. The other treasures, Kali-Yuga and Dvapara-Yuga, are linked to the holy sword. Kali-Yuga, a holy staff, is capable of absorbing different energies in order to strengthen Soul Calibur. Dvapara-Yuga, the holy mirror of the Ling-Sheng Su Temple, is used to help keep the purity of Soul Calibur intact and has the power of purifying the corruption of Soul Edge.
Krita-Yuga had been stolen from the temple by one of the monks, Kong Xiuquiang, and handed to his lover Chai Xiangfei, the mother of Xianghua. She will inherit the battered sword, unaware of its original form. Eventually she, alongside Kilik, fought with Nightmare at Ostrheinsburg Castle, and used the holy blade to shatter Soul Edge. However, Inferno, the evil will of the blade, took Soul Calibur and plunged with it into an abyss of his own making.
Although it is not clear if it is canon or not, if the Evil Soul Calibur ever existed, it would have been created in the void of Chaos, shortly after Inferno's defeat at Xianghua's hand, when the sword of light is lost in the abyss created by Soul Edge. Surrounded and consumed with the ambience of evil from the Soul Edge and Inferno's flames, the Soul Calibur eventually succumbs to the darkness and bonds with Inferno.
However, when Nightmare almost completed Soul Edge, Raphael Sorel appeared and pierced the eye of Soul Edge during his battle against the Azure Knight. It was weakened considerably. Soul Calibur was freed from the darkness and so was Siegfried Schtauffen, who regains sanity. Soul Calibur appears from where it was trapped within the cursed blade, and Siegfried drives it into the core of Soul Edge. Now both blades are silent, seemingly powerless, locked in a fateful embrace.
Time passed, and eventually Siegfried and Nightmare met at the Lost Cathedral. A ritual induced by Zasalamel broke the embrace of souls and each sword was freed from the grasp of the other. Nightmare grasped the Cursed Blade while Siegfried took the Spirit Sword. The swords clashed, causing a great cataclysm destroying the cathedral and breaking the two contrasting warriors apart from one another and injuring them both severely. Saved and sustained by Soul Calibur, Siegfried drew a strong connection with the blade, with his armor covered in crystals that match the sword. Siegfried pursues Nightmare toward Ostrheinsburg, seeking to finally atone for his sins, with the spirit sword firmly in hand.
It is currently in the possession of Tokaru.