Since Ven and Kairi are both thought to have hearts of pure light, they could have a bigger connection. Just like Namine has something to do with Sora, Roxas could have something to do with Kairi. Instead of becoming part of Sora, Ven could have become part of Kairi through experiment and then rubbed off on Sora's nobody. and that could be why Roxas and Kairi were able to connect in KH2. Hmmmm?