Quote Originally Posted by Sephiroth View Post
You can see the realm of darkness at the end of Kingdom Hearts II. Sora and Riku arrive at the dark side of the Destiny Islands. Then they get back to their side, the light side after they have found Kairi's letter from the light side.
*Echem.* Did you not read the reports? They weren't actually yet in the Realm of Darkness. They were in the "In-Between" staring at the Sea to Darkness. So we haven't actually seen the Realm of Darkness yet.
I would expect it to be much tougher... also, if Mickey's Kingdom Key of Darkness cannot defeat bosses in the Realm of Light, I would expect the same to be true of Sora's Kingdom Key of Light fighting bosses in the Realm of Darkness, thus needing a cooperation attack with Mickey to finish them off.

It is true Xemnas wanted to get even more and more powerful. Just because the other characters have fused with their other side it doesn't mean Xemnas just needed to fuse with "Ansem". Also there would still be a missing part: The body. Sora and Kairi could fuse with Roxas and Naminé because they are not just Heartless and Nobodies. Sora got a new body because of Kairi and Kairi still had her body because she was connected to Sora when she had lost her heart so her heart was not controlled by her own darkness to form a heartless of it. But Xemnas and Ansem are a Nobody and a Heartless. Of course Ansem has a new body because of Riku but he has not his own body. Ansem (while controlling Riku) and Xemnas have never met. So they never had the chance to fuse even if it would work.
(SPOILER)We now know the truth of Roxas. I'm still curious about Naminé though. Anyway, yes, Ansem (Xehanort) and Xemnas (also Xehanort) were separated not only in spirit but by distance as Xemnas (through transportation via the Dark Corridor) arrived in what would become the World That Never Was with his colleagues. Therefore, the two have never met. But neither would they care. Xemnas hoped to discard his former identity tied to his original heart and that having a new heart would make him stronger.
Also I do not believe Roxas really has emotions just because he is "special". You can see emotions of almost everyone in the Organization XIII because Nobodies just act like they would have feelings and because it is difficult to make a whole story with boring, emotionless characters.
Actually, as stated above most of the Organization act emotion based on memories of whom they once were. Roxas begins to show signs of emotion even before he starts to remember who he is. I'm pretty sure that's because Sora's heart is one that has been purified by Kairi and his emotions transmit like morse code over to Roxas as they are both connected.