One hundred years prior to the events of the movie, a Hoopa appeared in Dahara City and often battled other Pokémon summoned through its rings and defeated them to showcase its strength to the people in town. As it soon became more arrogant, it soon summoned Legendary Pokémon to showdown with to further showcase its strength and powers. At first, Groudon was summoned along with Kyogre, and engaged in a three-way showdown between it, Kyogre, and Hoopa. It was soon driven into Hoopa's rings and defeated along with Kyogre.
When Hoopa's rage over having its power sealed for so long manifested as a shadow, the shadow Hoopa summoned Groudon, now in its Primal form, along with Primal Kyogre, Dialga, Palkia, Giratina, and Kyurem and was controlled by Hoopa to fight Mega Rayquaza, Mega Latias, and Mega Latios. It roamed the town, attacking Mega Latias and Mega Latios, firing Flamethrower at them several times. It was also frozen by Kyurem briefly, but the intense heat coming from its body unfroze it. Later, when Hoopa's power was tamed, Groudon was freed from the shadow's control. However, due to the violent clash between Legendary Pokémon, time and space were warped and slowly began to consume Dahara City. While Hoopa helped the townspeople escape, Groudon joined the other legendaries in attacking the space-time distortion to hold it back while everyone escaped. Once all had been saved, Groudon returned to its home along with Kyogre.
