My guess is that the BHK's partners are Riku and Mickey because in ASAS Riku (BFU) and the BHK (DWU) were fighting together. I know ASAS is a concept video so don't try to remind me. Mickey will most likely be with Riku because they left Castle Oblivion together in COM.
Another reason why they might be partners is because they are all might be Twilight. I know Riku is Twilight, but Mickey and the BHK are questionable.