Plot:
Around one hundred years ago, in a desert town that would become Dahara City the Pokémon Hoopa Unbound appears boasting how strong it is. It summons Kyogre and Groudon from its interdimensional rings. Hoopa Unbound battles them back and impresses the townspeople. Hoopa Unbound asks the townspeople if they were surprised. When Hoopa Unbound appears again, he summons Reshiram, Zekrom, and Regigigas. The battle between all the Legendary Pokémon begins to destroy the town. The townspeople cry out to stop, but Hoopa Unbound is determined to show off his power. Suddenly, a man appears with an Arceus necklace around his neck. The man holds an item called the Prison Bottle. Hoopa Unbound is sucked into the bottle. The man saves the town and halts Hoopa Unbound's rampage.
Years later, Baraz is searching for the Prison Bottle in Arche Valley. In a cave, after using Solrock's flash to see, he discovers the bottle. He is delighted and grabs the bottle. However, Baraz gets possessed by the dark power within.
Meanwhile, Ash Ketchum and his friends Pikachu, Serena, Clemont, and Bonnie are relaxing at a Pokémon Center near Dahara City. Ash and Bonnie swim. Clemont works on an invention. Serena brings out donuts for everyone. While they enjoy the donuts, they begin to disappear into Hoopa's portals. Ash finally spots the arm reaching out in time to grab hold. Ash and Pikachu are pulled through Hoopa's portal. They find themselves on the other side of Dahara City with Hoopa. Hoopa asks if they were surprised. Ash says that he is very surprised. Wanting to delight Ash even more, Hoopa names Ash Ashkan and Pikachu Pikan. Hoopa opens two portals, where hundreds of Pikachu come through. This includes a full set of cosplay Pikachu. Ash is startled to see so many Pikachu. When Hoopa quizzes him on which one is his own, Ash finds Pikachu within a single moment. Hoopa seems let down that Ash did not have a harder time.
Meray appears, and tells Hoopa to return all the Pikachu it "borrowed". Pikachu gets up on the railing to command all the other Pikachu to return, which they do, impressing Hoopa. Meray introduces herself as one of the caretakers of Hoopa. Ash then drags Clemont, Bonnie, Serena and all their stuff through the rings. They decided to visit the tower and thought it would be easy to go through the rings to get there. However, only Hoopa is unable to pass through its own rings. They decide to walk instead of passing through Hoopa's rings.
Baraz arrives on his Braviary and instantly opens the Prison Bottle. The darkness envelops Hoopa, who transforms into Hoopa Unbound. Baraz returns to normal, and both he and Meray are very happy to see that Hoopa Unbound got its power back. But Hoopa Unbound instantly begins to smash things, its tail destroys a doughnut shop, and it throws a piece of a building at the heroes. Pikachu counters with Thunderbolt destroying the piece and accidentally blasting Team Rocket off again as they were plotting to steal the bottle.
They get Hoopa Unbound's power back into the bottle. Ash and his friends quickly learn that by touching it, they will be possessed by the evil power within the bottle. Clemont happily shows off his new invention. It is a device that can hold the bottle up with electric waves. The device carries it in his Aipom arm, which prevents anyone from touching it. Hoopa is absolutely terrified of the bottle and the power inside of it by shaking and whimpering.
They sit down to eat. Baraz explains Hoopa's story. One hundred years ago today, Hoopa Unbound began to appear in the town. Hoopa Unbound ate the food and caused problems. The townspeople came to love it when he would battle Pokémon to entertain them. Hoopa Unbound made the townspeople very happy. It also brought much gold. Dahara City grew from a tiny village to a great city. Only when it began to summon more powerful legendary Pokémon and grew more obsessed with showing off its power even if it destroys the town, the townspeople had to do something to stop it.
The man who stopped Hoopa was Meray and Baraz's great grandfather. They show off their Arceus necklaces, and Ash thinks he recognizes them. Clemont explains Arceus is the one who is said to have created all things. Meray and Baraz explain how their family is connected to Arceus' power. They tell how their great grandfather could use it to control Hoopa, who would throw great tantrums screaming for him to give back its power. Meray and Baraz grew up with Hoopa like siblings, getting into mischief and playing together, even healing Hoopa when it grew very sick when taken to Arche Valley. It is clear that they love Hoopa as family. They taught it many things about helping others and getting along with people. Their great grandfather accepted Hoopa as family.
Team Rocket appears in their balloon, thinking the Prison Bottle will up their Pokémon. The instant Meowth takes hold of it, though, he becomes possessed, and opens the bottle to unleash Hoopa Unbound's power. Hoopa fights the power, too afraid of vanishing if they become once again, and is able to keep it at bay, but Hoopa Unbound then develops as a separate Pokémon. In the struggles, the Prison Bottle explodes. Hoopa summons Lugiato fight Hoopa Unbound after Team Rocket is blasted off and Baraz's Braviary is defeated. Lugia distracts Hoopa Unbound as they make their escape.
Meray and Baraz know that they can make a new bottle at the tower with the power of earth, fire, and water. They decided to use Serena's Braixen, Ash's Frogadier, and using a ring, Bonnie goes to the desert to ask for a Hippopotas' help, and bring it along. Ash stays with Hoopa while the rest head over to the tower to make a new bottle.
While hiding from Hoopa Unbound, who is still fighting Lugia, Ash and Hoopa begin to talk. Hoopa promises that once strong enough, it will make any of Ash's wishes come true. Ash says that his wish is to become a Pokémon Master and Hoopa says that it will make it happen. Ash refuses, though, saying that is a dream he plans to attain by himself. Hoopa is absolutely shocked that Ash plans to attain his own dream without using any rings or magic wishes. Ash talks to Hoopa about how this Hoopa Unbound seems to be a shadow of Hoopa, and it needs to learn to make with itself to solve this crisis.
Hoopa Unbound appears in a ring and searches for them with its giant hand. Right when they were about to be caught, Lugia appears and carries them away on its back. Hoopa Unbound tricks Lugia into flying into a ring and sends it back to its ocean home. Ash and Hoopa are powerless. Hoopa summons Latias, Latios, and a shiny Rayquaza. Ash, Hoopa, and Pikachu ride on Latias and Latios, while Rayquaza helps to battle Hoopa Unbound. Ash commands the Pokémon to attack, but Hoopa Unbound summons Primal Groudon, Primal Kyogre, Dialga, Palkia, Giratina, and Kyurem.
At the tower, the others are hard at work making a new Prison Bottle, using the powers of fire, earth, and water. Clemont commands Frogadier, Bonnie commands Hippopotas, and Serena commands her Braixen, while Meray and Baraz use their powers. The bottle begins to form.
When the six legendary Pokémon summoned by Hoopa Unbound begin to attack, Latias, Latios, and Rayquaza all Mega Evolve. Kyurem becomes Black Kyurem and then White Kyurem as the all out brawl continues over the city. Mega Rayquaza creates a twister around Dahara Tower to protect it. The others reforge the Prison Bottle. However, Hoopa Unbound and the legendaries break through the twister. The bottle is made again, but Baraz drops it. Ash catches it but gets possessed by the evil within. Shadow Ash plans to destroy Hoopa, but Hoopa tries to cleanse him with his happy memories. Ash returns to normal and realizes that the evil is gone. All the legendary Pokémon roar. Hoopa states that they were surprised. However, due to too many legendary Pokémon being summoned, a void warp was formed around the tower. All the legendary Pokémon could not stop it. Hoopa transforms into Hoopa Unbound and lets everyone escape. At the end, Meray and Ash leave with only Baraz and Hoopa left. Baraz and Meray try to help Hoopa escape. Arceus temporarily slows down the void warp. Hoopa remembers the words of the traveler who happens to be Baraz and Meray's great grandfather and considers Baraz and Meray family. Hoopa decides to stay with them. Hoopa finally manages to go through the ring with Baraz at the last second. At the end, the void warp leaves a decimated tower and city. Arceus leaves through the clouds. All the other legendary Pokémon return to their homes. At the end, Clemont suggests going back to Arche Valley. Hoopa declines and says that he has unfinished business. Hoopa wishes Ash the best on becoming a Pokémon Mister(Pokémon Master). In the credits, Hoopa Unbound is shown rebuilding the city by helping the construction workers with his strength and his rings.
Source: https://en.m.wikipedia.org/wiki/Pokémon_the_Movie:_Hoopa_and_the_Clash_of_Ages
Source: https://en.m.wikipedia.org/wiki/Pokémon_the_Movie:_Hoopa_and_the_Clash_of_Ages