
Once the Straw Hats entered the island, they saw a giant skull (bigger than a giant) burning in flames and a few panels after that they saw an actual dragon. We got confirmation of that in chapter 989, when Big Mom sees the Numbers in Wano: apparently Kaido bought them from Punk Hazard. So there is a link between the Oni race and Punk Hazard. The first thing we see before entering the island is a plate with three logos: the Marine logo, the World Government logo and a “Oni Skull” logo, that resembles in a peculiar way the giant skull in Onigashima. It is the arc that starts the entire Kaido/Wano storyline. We should not forget that this is the very first island of the New World, and so it must be very important. But also Yeti Cool Brothers, prisoners in the ice, and so on. Some of the stuff that was set up in this arc has not paid off yet, most of that having to do with Vegapunk and his experiements on dragons, gigantification and devil fruits. Its original appearance has also been conveniently hidden under magma and ice.

We’ve seen the clash of the Admirals and a brief Vegapunk/Caesar flashback, but nothing more. Punk Hazard has always been one of the strangest islands we’ve ever visited, because its history is unclear.

And Onigashima seems to be a cool way to close that hole. But basically the reason why I believe this, it’s because it’s a doughnut shaped island with a missing hole inside. This would also justify the existence of the rear entrance. If we look Punk Hazard from above we see the central lake connected to the sea via two canals. So, can we find in some island we’ve already seen a missing circle shaped piece? We’ve seen that Onigashima is basically a circle, with a front and a rear entrance (this rear entrance by the way has no reason to exist…). I’m saying this because it could be use as a precedent and the same “puzzle” logic could be apply in this case. It requires us to look from above, at an island level, while we are small and lack the wider perspective.

I thought it was brilliant, because it was such a simple solution yet it was almost impossible to guess it in advance. When Nami finally puts together the map of Jaya and Skypiea and realizes that they were once the same island. But one that comes to mind is the Skypiea reveal. If you’d ask me “What is your favourite reveal in One Piece?” I would need to think about it. For this reason I think it would be more impactful if we already knew the name of the original location, or even better if we’ve already been there with the Straw Hats and we haven’t even realized it. If the key to understand the secret of Onigashima is in its name, it would be strange to set up expectation for a name that we haven’t even heard once in the story. But even if that’s the case we still don’t have a name for “Kaido’s favourite island”.
