That was only because Xehanort extracted, by force mind you, all the darkness from his heart to make him. Considering Vens kind nature, I think its safe to say Xehanort could do the same to literally anyone and they would have their own Vanitas if you catch my drift.



Besides, just because Vanitas is pure darkness doesn't necessarily mean he's evil. The only reason he acts that way is because of the circumstances surrounding him after his 'birth' which is expanded upon in the novels.