Probably in what he was at the last battle against Hashirama. After all, Hashirama is sure that he killed him, so it really might be a half-truth.
Well, Obito wanted to become it's jinchurki in the form it is now, but Kakashi jumped out and Obito had to take care of him... oh right, it seems that Yahiko Pain is stronger than Obito, or perhaps Obito was tried from battling this whole day and night ? Of course it could also be explained that Kakashi is simply the worst enemy Obito could have get.
Madara becoming Jyubi's jinchurki might be a good reason why the alliance will need over 10 Kage-Level Nninjas .
Oh right, I forgot to mention how surprising it is, that this story follows what happened in the latest Narutomovie: