Balloons, Brionne, and Belligerence! (Japanese: アシマリ、オシャマリ、いかりのダダリン！Ashimari, Osyamari, and the Anch-gry Dadarin!) is the 40th episode of the Sun & Moon series, and the 979th episode of the Pokémon anime. It first aired in Japan on August 31, 2017 and in the United States on November 18, 2017.
After having little success using the Z-Move Hydro Vortex, Lana and Popplio meet Ida and her Brionne, who use the Z-Move as part of their show and agree to take Lana on as an apprentice! Lana and Popplio train hard—and when Ida’s sweetheart Kanoa returns with reports of sunken treasure, they join the expedition.
The treasure is guarded by a Dhelmise, who’s already annoyed after a run-in with Team Rocket and traps Kanoa’s boat in a powerful Whirlpool. Brionne goes up against it and loses, but after all that training, Popplio is ready. It uses Hydro Vortex to counter Dhelmise’s Whirlpool and send it far away!
Ash and Mallow visit Lana at her house to check on Popplio after its attempt to perform Hydro Vortex the previous day failed. Walking along the beach, Lana suspects it may have something to do with Popplio's lack of battling experience. Their attention is soon drawn to a crowd nearby, where Ida and her Brionne are putting on a performance. Ash, Lana, and Mallow watch as Brionne releases multiple colored balloons while Ida gets ready for their last act. Kanoa is out at sea nearby with a surfboard as Ida and Brionne perform Hydro Vortex, creating a whirlpool for Kanoa to surf on. The performance ends with the crowd amazed, and Lana declares she wants to be Ida's apprentice.
Lana explains to Ida that she is keen to use a Z-Move and with encouragement from Kanoa, Ida agrees. Ida explains a little about themselves as Kanoa says that he is a treasure hunter and is currently pursuing a lead on some treasure. He brings out some documents on a ship that sunk nearby with its cargo lost. Later, after Kanoa leaves on his search, Ida starts training with Lana and starts with strength training as has Brionne make a balloon. Ida instructs Lana to have Popplio pop the balloon with its own balloon but every attempt results in Popplio's balloon popping. Later as the sun starts to set, Ash and Mallow watch as Popplio tries to pop Brionne's balloons with no success. With Popplio growing tired, Ida calls it a day as Kanoa returns having had no success.
Before going home, Ida gives Lana some encouragement which Lana thinks about that night. The next day, Ida and Brionne continue to perform as Ash and Mallow encourage Lana as Kanoa continues his search. Soon Popplio's balloons improve but fail to pop Brionne's but is soon able to pop them as Kanoa arrives, having found a good lead. He has found that the treasure is Mystic Water which helps to enhance Water-type moves and Kanoa allows them to join him in the search, unaware that Team Rocket have been listening nearby. The next day, they set sail and arrive in the area that was indicated. Kanoa's plan to search the bottom of the ocean is to use one of Brionne's balloons and Brionne surrounds Kanoa with a big balloon and he jumps into the water with Brionne assisting.
Underwater, Kanoa soon spots the sunken ship but as he approaches, he spots a Dhelmise and returns to the surface. Informing the others about Dhelmise, Kanoa and Ida know a way of approaching as Team Rocket spy on them from their new Bruxish submarine. They dive down to the ship and get ready to seek the treasure only to be stopped by the Dhelmise. Team Rocket aren't happy to be stopped but as Dhelmise demands they move away, Meowth convinces it that they were put up to it by those on the surface. Team Rocket back off as Dhelmise heads for the surface. As Kanoa and Brionne get ready to try again, their ship is attacked by the Dhelmise causing Kanoa to move the boat away. Dhelmise stops the boat from moving and starts to drag the boat down. As Team Rocket watch Dhelmise, Jessie takes the opportunity to get at the treasure.
On the surface, Ash has Pikachu attack Dhelmise, which doesn't work so Ida gets Brionne to attack which frees the boat from Dhelmise. As Brionne heads back to the surface, it is attacked by Dhelmise and is knocked out as Ida requests Kanoa get them to the Pokémon Center only for Dhelmise to surround the boat using Whirlpool. Team Rocket are sawing through the sunken ship, only to be caught up in the Whirlpool. As Team Rocket try to break free, Bewear arrives to rescue them. On the boat, things are looking bad but Popplio becomes determined and Lana decides to use Hydro Vortex to reverse the Whirlpool. They perform Hydro Vortex which collides with the Whirlpool which sends Dhelmise flying. Later they watch as Kanoa returns to the surface having retrieved the Mystic Water. Kanoa gives it to Ida and puts it around her neck as a thanks for all of her hard work. Back on shore, they bid their farewells, hoping to see each other again in the future.