Board Thread:Questions and Answers/@comment-25801533-20150531094407/@comment-25152698-20150531160951

I think it may have been another speculation between Kein Shiba and Ichigo Kurosaki. All the captains have done this at one point, if not all the shinigami. It's very likely that Kurosaki-kun is even Kein's reincarnation; this would explain how Ichigo is so naturally adept with his skills, beyond being only a crossbreed.