Ok here's my theory. You all know that the clothes Master Xeahnort, the masked figure in BBs,and transformed Riku all look alike? I think there's a name for people like them. People who have stepped into the realm of darkness amd used its powers. But not just any people, Keyblade weilders. Those with strong hearts that can use so much darkness without being consumed. Then there's Sora's Antiform which highly resembles the shadow heartless he once became. But like Xeahnort he was a keyblade weilder and kept his state of mind, even Riku when he was engulfed by Ansem. Plus I know Sora a strong dark side. In the beginning of KH that strange voice said,"the closer you get to the light,the stronger your shadow becomes". Plus Sora lost his light in becoming a heartless and used Kairi's light,"a princess of heart with no darkness in heart" to bring him back. Im not sure, but you gotta admit,it's the one thing i see that Riku and those guys "excluding Sora" have in common. What are your thoughts? Again im not about any of this.