I didn't really have much else to do back in Onigashima, so I used to try and get my hands on all the books I could about the outside world.

[ but kaido was never one to collect a lot of books... but yamato managed. ]

So I ended up reading one about that described different traditions around the four oceans — North Blue, West Blue, South Blue and East Blue. I mean, there's Grand Line too, that's where I'm from, but I was more interested in learning about the Blues since I've never been, and Oden's logbook didn't describe them either. Anyway... I learned that where all the Blues have some of their own traditions, they mostly vary island by island. The same as in Grand Line.