User blog comment:CoolJazzman/Why do you think Yamamoto wasn't giving a promoted to become a royal guard./@comment-6342763-20130420222438/@comment-5551986-20130423224033

Ouetsu Nimaya did invent Zanpakuto, I have a feeling he is the oldest shinigami? Or Osho. If Yamamoto and friends were using Zanpakuto back in those times, Ouetsu must have been his senior. Tenjiro Kirinji seems to know Unohana well and taught her Kido. I would bet that they were part of Yamamoto's original Gotei.

The Oken could be a way to attain everlasting youth? But not immortality.

Had a dream that the Oken was actually a "holder of data" and could be passed on, giving the receiver the knowledge of their predecessor, the history remains, their body dies.