Merilyn Flame, a cunning jewel thief, relentlessly pursues the legendary Diancie to harness its diamond-forging powers. Competing against rival thieves Ninja Riot, Millis Steel, and Argus Steel, she clashes most fiercely with Riot, whose aggressive tactics oppose her calculated approach. Her trusted partners—Delphox, wielding fiery assaults like Flame Charge, and Yanmega, enabling swift aerial maneuvers—aid her heists.

Though driven by ambition and prone to confrontation, Merilyn’s dynamic with Riot unveils unresolved romantic undertones. Their rivalry culminates in Allearth Forest, where a reckless skirmish accidentally awakens Yveltal. The Destruction Pokémon’s Oblivion Wing petrifies her Delphox and Yanmega, leaving Merilyn moments from sharing their fate. In her final seconds, she drops her guarded facade, embracing Riot in a fleeting moment of vulnerability before turning to stone.

Resurrected by Xerneas’s life-restoring energy, Merilyn renounces thievery, her priorities reshaped by loss and connection. A post-credits scene reveals her working at a boutique, where Riot visits to propose marriage—a symbol of her reformed life and commitment to honesty. Her journey reflects a stark evolution from ruthless ambition to redemption, forged through catastrophe and unexpected emotional ties.