Gotcha. Still not 100% on it, but I can't back it up since there I don't have enough facts on my side.
Also nobody or not, I wouldn't be too surprized if Riku and Axel do have some sort of relation.
1. It's pretty obvious Sora-Roxas-Ven are connected. Even if one wants to say Ven isn't connected to Sora, he is connected to Roxas. Nomura did hint that if Ven has a connection to Roxas, that he might have a connection ro Sora too.
2. Kairi-Aqua-Xion is not as obvious. A lot of people are saying Xion has a connection to either Kairi or Namine (if she has a connection to one, then there's a fair chance she has a connection to the other). Aqua's the only one that might stand out other than being the only girl, although one may be able to say they're all connected due to being Keyblade wielders, or at least wielded a Keyblade at least once.
3. Riku-Terra-Axel is partially argueable. The most arguable part is Riku and Axel, mostly they're connected to the protagonists Sora and Roxas as best friends. Riku and Terra have the obvious connection due to being the only two protagonists to willingly take control of the dark. Axel does have some control of the dark, as do most Organization members, but is seperated from the two by not being shown to wield a Keyblade.
Sora, Riku, and Kairi are connected.
Roxas, Axel, and Xion are connected.
Ven, Terra, and Aqua are connected.
Sora, Roxas, and Ven are connected.
Riku and Terra are connected. (From examples stated above. Because it is known that Riku is in BBS, there may be a bigger connection. There might not be.)
Kairi and Xion are (probably) connected.
Based on these, it's not impossible to imagine though all of these connections, that they all have some relation to eachother. It seems to be a common theme. The person related to the protagonist has a male best friend and female best friend, and these friends have connections to at least one counterpart in another trio. For those reasons I believe, Nobody or not, Riku and Axel have some form of a connection.
I'm going by the thread title, so this post should still apply to the thread.