In Soul Calibur IV, in Cassandra's Story Mode, the character Sophitia appears possessed by Soul Edge after being convinced by Tira to surrender her soul to the sword. She fight alongside Azola and Dürer, and after is defeated by Cassandra, she returns home with her.
Sophitia's possession is similar to her daughter Pyrrha when is turned into Pyrrha Ω.
Probably Sophitia's possession never took place, due do the fact that it wasn't mentioned in any other Story Mode.
Dark Sophitia can be created in Character Creation mode, being just a palette edit with the weapon Soul Edge.