What lies in his soul is Revenge. Nelo Yuuki is a character that apperars in SoulCalibur III and SoulCalibur IV he is the son of Victoria and Alexander (his Fahter was one of the Primordial Angels and his Mother was a human) they both were killed for their relationship his father was killed in an audiency by the society of heaven, and his mother was killed trying to protect him. He swear to revenge his family and kill all the angels specially those from the Society for that he now works as a mercenary killing both Angels and demons and the like as part of his revenge.