What are you on? It's OBVIOUSLY Namine!!
Heres my theory-
After CoM Namine went off with DiZ right? But this is the bit Nomura didn't reveal, Namine was actually killed by Larxene at the end of CoM and the character that we THINK as Namine in Days and KH2 is actually Larxene in disguise, WHO FAKED HER OWN DEATH. Why? To take over Kairi, and she became one with Kairi at the end of KH2. However, DiZ, who realised the current Namine was a fake sent her BACK IN TIME, in order to ensure her survival. However, being in a time when Kairi is whole has caused Namine to go insane, merge with Obi-Wan Kenobi to become Obi-Wan Namine.
And thus, this is what happens. Fullstop, end of discussion, no matter what you say you CAN'T PROVE ME WRONG.