So the admiral-fight taking place on this island-theory was actiually correct lol.
Good to finally know how Vegapunk was involved in how this island got it's name + It explains the gate & fence.
As for the baddy in the story... It's pretty obvious now that it's all his doing. (Samurai as well as creatures)
He an old vegapunk-rival or (perhaps failed) experiment that give hims his form/powers w/e they may be?
I can see they guy using a Shishibukai's name when comitting crimes, maybe that explains the samurai's words?
Or, even though unlikely, he might actiually be one of the new shishibukais....