Merilyn Flame is a jewel thief determined to capture the Mythical Pokémon Diancie and exploit its diamond-creating abilities. She partners with Ninja Riot and commands a Delphox. Launching their pursuit in Avignon Town, they initially attack Diancie. During one confrontation there, Merilyn commands her Delphox to unleash Water Pulse and Thunderbolt against Ash and Pikachu. After Diancie escapes with Ash's friends, Merilyn continues the persistent hunt through urban environments and forests. In Orsay City, she separates from Riot to ambush the group, engaging Ash in battle while Riot pursues Serena and Bonnie. Merilyn later reunites with Riot during a forest encounter, where they corner their target until other characters intervene. Her relentless chase after Diancie inadvertently fuels disturbances that escalate the film's central conflict involving Yveltal. Merilyn's character design incorporates elements intended to appeal to adult audiences within the franchise's aesthetic. Her motivations remain consistently focused on acquiring Diancie's power for personal gain throughout the narrative, without evolving significantly or revealing backstory beyond this primary objective.