Revealed Secret - The Truth of Ancient Weapons

With Hody and his officers caged, the royal family decides their punishment while the Straw Hats slip away to avoid being lionized. Jinbe gently turns down Luffy's offer to join, promising to enlist once his lingering obligations are settled. Neptune catches up to them by Den Den Mushi and lures everyone back for the grand banquet he had always intended, complete with the diva Maria Napole, Mermaid Cafe dancers, and oceans of food and drink.

As the revelry winds down, Robin draws a tipsy Neptune aside and asks about Joy Boy. The king, startled that she can read poneglyphs, explains that Joy Boy was a Void Century figure from the surface whose written apology to the Mermaid Princess concerned a broken promise tied to guarding Noah. He confirms that the ability to command Sea Kings passes through the Mermaid Princess line, both then and now.

Connecting this to a poneglyph she read in Skypiea years earlier, which placed an ancient weapon on Fish-Man Island, Robin deduces that the princess of Joy Boy's era shared a second name with Shirahoshi. That name is the ancient weapon Poseidon.

The royal family frees Hody's human slaves and seals off the Fish-Man District permanently. Jinbe declines Luffy's invitation for now but vows to return. The promised banquet proceeds at Ryugu Palace. Robin questions Neptune about Joy Boy and the Mermaid Princess legend, learning that the princess could control Sea Kings. She concludes that Shirahoshi is the reborn ancient weapon Poseidon.

The episode introduces Maria Napole, Blakey, and Miles. The anime adds Zoro echoing Luffy's quip about not wanting to share booze as a hero, a near-toast from Neptune that Luffy interrupts, extra banquet appearances for the Medaka Mermaid Quintuplets, and a reunion greeting between Ishilly and Camie. The preview for the following episode runs shorter than usual.