If he was sent back in time because he was here before, then the only reason he was sent is because he was sent. The action causes itself to take place. If he hadn't been sent, he wouldn't have been sent. This, once more, causes a paradox, and destroys the universe. Or causes time to crack. I dunno. Whatever is most amusing and opens the most amusing path for the roleplay to take, I guess.
Personally, I like the second theory the most. We've already discussed what future he comes from, but because of his actions that very same future can be avoided, which would be rather amusing. If this future can NOT be avoided, then this entire fight has no point to it whatsoever because we all know Kami will win. As such, I vastly prefer a model in which the future is not set in stone. Rather, knowledge or interference from the future can cause that very same future to change.