Damn you, LilDrino!
His name would be Kurix and (no-brainer) he would be the Nobody of Riku and Number XV of the Organization. He would come into existence when Riku is killed by Number XIV, and he would then charge at Sora and Kairi barehanded. Sora then beats him away with Riku's Keyblade before it vanishes. Riku is later brought back by Master Xehanort, because he wants revenge on SRK in one fell swoop, because of their connection to TAV.
He would be about an inch taller than Riku, and more muscled, and his skin colour would be the same as Riku's but lacking a little colour. Green eyes like Riku's but a little greyed. (Off topic for a second: XIV would have power over the mind, can erase memories and control things telekinetically) Kurix element-thingy would be strength (the bodily, physical kind) and his weapons would be clawed and spiked gloves like Cloud's in KH1 and spiked boots. Hair style is like Axel's, but shorter and silver.
Dislikes having to team up with people unlike him, hates full-beings. Avoids working with others, but eventually opens up to XIV, because he enjoys having someone to talk to. Pities Riku, Kurix sees him as very lonely.
Would post a picture, but my picture posting never works; and I can't be bother drawing/painting him in real life or a studio program, just saving my money to buy a program called Poser 7.0