Riot operates as a secondary antagonist in the film, a ninja and jewel thief who doggedly pursues the Mythical Pokémon Diancie. His goal is to exploit her diamond-creating power for personal profit, frequently clashing with rival thieves Marilyn Flame, Argus Steel, and Millis Steel. Riot relies on stealth and deception, hiding within trees or employing his Greninja's invisibility during attacks.

He primarily uses Greninja to capture Diancie, commanding moves like Water Shuriken and Double Team to generate clones in battle. For aerial transport, Riot attaches himself via ropes to multiple Ninjask. His initial dynamic with Marilyn Flame is fiercely competitive and hostile, centered on controlling Diancie. This rivalry shifts dramatically when their fighting awakens Yveltal from its Cocoon of Destruction. After Yveltal petrifies Greninja, Ninjask, and Marilyn's Pokémon with Oblivion Wing, Riot comforts the distraught Marilyn, revealing a concealed affection moments before Yveltal petrifies them both.

Revived by Xerneas's Geomancy, which restores the forest and its inhabitants, Riot appears in the film's closing scenes. Now formally dressed, he visits Marilyn at her workplace and proposes marriage, signaling a decisive move away from his criminal life towards a committed personal relationship.