I've figured it out!!

[Shadow Skill]

The only good theory I've heard of Yondaime-is-akatsuki's-leader is that when the Shinigami sealed Kyuubi it sealed only a part of Yondaime... leaving his dark side behind.

Oh... and the leader is red-haired, not blond.

WHAT!?!? NARUTO HAS SHINIGAMI!?!?!?

I never noticed anyone running around with a Zanpakutou in Naruto. :/