AquaRox23

Most of the reason why Roxas and Ven look and are similar is because they are one in the same. Upon completing Ven's story Ven's heart is lost due to the darkness being defeated (Vanitas) Ven says as he is floating he feels a fimilar warmth and he is in "his" heart. That person can only be Sora. Sora was the only of the 3 NOT to have the power of a keyblade passed over to him. (Kairi by Aqua and Riku by Terra) So the presence of Ventus in Sora's heart allows him to wield a light-based keyblade which also explains how Roxas looks exactly like Ven for even with Roxas using dark skills while in the organization he was still a light being and used light attacks. Terra is in a fight with Xehanort over his heart but during the fight Xehanort has control of his body which also expalins how in KH: II they said he just vanished about the same time of BBS if not a little bit afterwards. Aqua wanders the realm of darkness for 13 years or so due to the fact that BBS is 10 years before KH1. So if DiZ was met in KHII which was 2 years after KH1 then that would show that. So no AquaxTerra because if you played all 3 stories Sora lived while Aqua, Ven, and Terra were alive just in chibi form.