A long time ago, Volcanion first met Magearna at the Nebel Plateau. The two became friends, as Magearna was able to fold up to protect herself whenever Volcanion exploded. Since then, Volcanion had been protecting Magearna at the plateau.
In the movie, Volcanion first appears chasing after an airship driven by Cherie and Levi. Volcanion states that he has come to retrieve something, but Levi fights it off with his Mega Alakazam and Glalie. During the battle, Levi manages to fit an electronic band around one of its legs, though Volcanion deflects a second band before it is launched off the ship. Volcanion then falls and crashes down to where Ash and his friends are. While Ash and the group are not severely hurt, they discover that the band that Volcanion had deflected earlier is now attached to Ash. Volcanion tries to leave, only for Ash to be forcibly pulled toward the band on Volcanion's leg. Despite its distate towards humans, Volcanion reluctantly allows Ash to stay by it as Volcanion flies off in pursuit of Levi and Cherie toward the Azoth Kingdom.
Volcanion appears at the kingdom where Alva is receiving Magearna from his henchmen. Volcanion confronts them but Alva begins to ward it off with his Mega-Evolved Shiny Gengar along with Alakazam and Glalie. Volcanion becomes frozen, but as it thaws, Ash's other Pokémon arrive and assist Volcanion in overwhelming the three Mega-Evolved Pokémon. The ensuing confusion allows Volcanion to escape with Magearna. Volcanion and Magearna then flee to Nebel Plateau, unwillingly bringing along Ash and the group.
The next day, Alva and his forces invade the Nebel Plateau, flooding the area with smoke. While Volcanion tries to retaliate, Volcanion and Ash become trapped by Electric Terrain and Stealth Rock. Alva's forces threaten Magearna that they will torture the humans and Pokémon until it submits and goes with them. Unable to watch its friends get tortured, Magearna surrenders and is taken to Alva. Angered, Volcanion, along with the group, goes off to the Azoth Kingdom to save Magearna.
At the kingdom, the group defeat Alva and his forces. However, they realize they had come too late, with Magearna having appeared to have lost her memory and personality. They also find out that the fortress they are in is spiraling out of control and will crash into the Nebel Plateau. The group then plan to explode the fortress in the air with Volcanion's power, while the rest flee in Kimia's airship. While Volcanion plans to destroy the castle from within the engine room, Ash refuses to let Volcanion carry the plan out as he realizes it will be a suicide mission. Ash tells Volcanion to explode outside so that it could escape as well. However, while Volcanion helps the humans and Pokémon evacuate the castle, after they leave, it jumps back inside, intending to sacrifice itself. Apologizing for not being able to save Magearna, Volcanion explodes once Kimia has completed the evacuation, completely destroying the fortress.
Later, as the others are mourning for its death, Volcanion appears injured, but still alive.
Personality and characteristics
Volcanion is very protective of both Magearna as well as the Pokémon living in Nebel Plateau. It would do anything it can to keep them safe from harm.
It also does not trust humans nor the Pokémon belonging to humans, and reveals that all the Pokémon living at Nebel Plateau were harmed by humans and thus fear them. However, over time, Ash and the group begin to regain Volcanion's trust for humans by bringing out their own Pokémon and helping to care for an injured Amaura. At the end, Volcanion allows the group, including the humans, to be called honorary Nebel Plateau Pokémon.