Necrid was once one of many warriors who managed to reach Soul Edge after beating its former owner. But as he approached the sword, the evil spirit of the sword, Inferno, raised from inside it and beckoned him. Upon seeing the apparition, the fear he felt was so great that he, despite thinking it was a dishonor for a warrior, escaped. He managed to avoid the confrontation, but ended trapped in the vortex of Chaos that Inferno brought. Trapped there, his mind and body were warped and contaminated by the strong evil aura of that realm, eventually turning him into an abomination.
During Kilik and Xianghua's battle against Nightmare, Necrid sensed that the spirit sword's existence harmed him, so he jumped through the open void and escaped Chaos just as it was collapsing. Now on the world once again, he soon discovered that he needed the evil influence of the void to keep himself alive. Out of instinct, and in constant pain, he attacked many travelers thinking they were "enemies", until one happened to carry a fragment of Soul Edge. The familiar aura softened his pain, and a "purpose" born in Necrid's mind: find the rest of the fragments so he can stop the pain. Necrid soon left on a journey to find other fragments.
Soulcalibur II Ending
His soul yearning for repose, Necrid sought the pieces of Soul Edge. At long last, Inferno appeared before him. A warrior's blood and his honor... long forgotten memories and reason reawakened within him. Victorious against the heinous Inferno, Necrid solemnly closed the opening to the void. And thus he disappeared into that darkness, taking with him the Soul Edge.