Giant Pokémon Island is located south of the Kanto mainland. Accessible only by ferry, the closest locations to this island are Fuchsia City to the north, and the Seafoam Islands to the west.
Half of the island is occupied by Pokémon Land, a theme park owned by Team Rocket's boss. The other half of the island, also known as Porta Vista, is comprised of two cities: Aopulco and Hatoba Port.
Tentacruel throws Meowth to the mangled Amusement Park with no memory of what happened, and whacks Nastina all the way to her cousin Brutella's wrecked restaurant in Aopulco. Then, all the jellyfish Pokémon retreat to the depths of the sea.
Hoping that the people of Hatoba Port remember the promise made to Tentacruel, Misty, her friends, and her new Horsea finally leave Giant Pokémon Island on a ferry boat. Following closely in a bucket tied to the aft is Team Rocket, tired, hungry, and defeated.
Horsea pleads with Tentacruel, only to be badly beaten for defending the humans. Ash, Misty, and Brock send their Pokémon to repel the onslaught, but the creature is just too big. Pikachu also tries to reason with it, to no avail.
Misty climbs to a high rise, and accepts responsibility on behalf of the humans. She promises that they will no longer threaten their ocean home, and begs it to stop. Tentacruel finally stands down and gives them a warning: "if this happens again, we will not stop."
The tidal wave brings with it thousands of Tentacool that decimate the city. The crowds seek refuge in an observation tower near Nastina's Amusement Park, which is also damaged in the attack. Tentacruel then speaks through Meowth via mind control.
The humans destroyed the coral reef and the ocean home of the Tentacool; seeking revenge, they will respond in kind. Misty realizes this is what Horsea was trying to warn them when they first met.
The Tentacool that used its energy beam on Team Rocket is bathed in the Stun Sauce, causing it not only to evolve into Tentacruel, but also to grow exponentially until it becomes a gargantuan creature. The giant jellyfish destroys the resort in an instant.
Nastina reacts by firing heavy artillery at Tentacruel, but the only thing she gains with that is to anger it even more. Tentacruel speeds towards the harbor, creating a tsunami that wipes away all the buildings in the seafront and beyond.
Team Rocket's plan is to pour their Super-Secret Stun Sauce on the Tentacool, and then catch them to sell in the fish market. Things take a dark turn, however, when they are surrounded by thousands of Tentacool.
With only one barrel of Stun Sauce, Team Rocket is unprepared for the barrage of the jellyfish Pokémon. One of them uses its energy beam to make the boat explode, but the barrel of Stun Sauce drops on its head, triggering a strange transformation...
Nastina makes a public announcement offering a substantial reward to whoever can exterminate the Tentacool. Misty is aghast when the whole town gathers at the harbor showing interest in Nastina's offer.
Chiefly among the crowd is Team Rocket. Showing up in their boat, they accept the challenge and head off to the man-made island where Nastina's Paradise Resort is in construction. A heartbroken Misty can't believe how everyone is disrespecting the ocean.
The survivors are taken to their boss: a property tycoon named Nastina. She thanks the heroes for saving her crew, and offers them money and food if they help her destroy the Tentacool that are interfering with the construction of her luxury resort.
Misty categorically refuses to harm the Tentacool, and storms off Nastina's place. Returning to the pier, Misty tells Ash and Brock that the Tentacool would not attack humans without reason. Ash wonders if Horsea's drawing in the water could be a lead.
Suddenly, a sand carrier vessel headed to a man-made island across the bay explodes. Misty sends her Staryu, Starmie, and Goldeen to help the crew of the sinking ship, while her friends find a boat to rescue the survivors.
One of the survivors screams terrified that he has to let his boss know what happened. Hiding under the pier, Horsea watches how the ship sinks and all work stops at the man-made island. Meanwhile, under the water, something lurks...
Ash and his friends are in Hatoba Port, the only city in the Giant Pokémon island that offers ferry service to the mainland, but the next boat will not leave for the next three hours. Sufficient time to find trouble!
Misty and Pikachu see a Horsea near the pier. The tiny dragon Pokémon shoots ink from its snout to make a drawing on the water. Noticing that it's injured, Misty tries to catch it to take it to a Pokémon Center in the mainland.
