Location from One Piece by Eiichiro Oda
Kaido's skull-shaped island fortress off the coast of Wano, site of the climactic Raid on Onigashima where the alliance of pirates, samurai, and minks toppled the Beast Pirates.
Onigashima is where empires fall. Kaido made it his seat of power — a fortress fitting for a man who called himself the 'Strongest Creature.' The Beast Pirates held their debauched Fire Festival here, a mockery of Wano's traditions, while planning to transform the entire country into a lawless pirate nation. The raid brought together over five thousand alliance fighters against thirty thousand Beast Pirates, Kaido, King, Queen, and the Tobiroppo. It was here that Luffy's Devil Fruit awakened as the Hito Hito no Mi, Model: Nika — the Sun God — and he defeated Kaido in Gear 5 while the island floated over the Flower Capital. The fall of Onigashima marked the liberation of Wano and the end of Kaido's reign.
A craggy island dominated by an enormous skull carved into (or grown from) the rock face, with two giant horns jutting from its crown. Inside the skull is Kaido's fortress — a vast cave system converted into a palace of debauchery where Beast Pirates feast, drink, and brawl endlessly. Massive torii gates line the approach. During the raid, Kaido used his powers to lift the entire island into the sky, floating it toward the Flower Capital as a threat. Fire, smoke, and battle scarred every surface.
Also known as: Onigashima, Skull Island, Kaido's Island