Mairin, a beginning Pokémon trainer from the Kalos region, bursts onto the scene amidst events tied to Mega Evolution. Her spiky maroon hair, fair skin, and bright orange eyes match an outfit of a yellow long-sleeved shirt, brown suspenders, dark green pants adorned with light green triangles, gray socks, and brown shoes. A light green cloak, a yellow-orange scarf, and a distinctive green hat featuring orange triangles and a yellow pompom complete her look, along with a small bracelet on her right wrist. Driven by an energetic, curious, and persistently cheeky nature, Mairin actively seeks adventure and displays fierce enthusiasm for understanding Mega Evolution. Despite repeated rejections, she tenaciously follows Alain, a trainer dedicated to researching the phenomenon, spurred by admiration for his skills. Her loyalty and protectiveness shine through, notably when she shields Alain from a Draco Meteor attack during a confrontation with Rayquaza. Moments of emotional vulnerability surface when Alain dismisses her as a burden or when her partner Pokémon, Chespie, falls into a coma after exposure to a mysterious energy linked to Lysandre's experiments. Her journey starts after receiving Chespin from Professor Sycamore. While traveling, witnessing Alain battle a Mega Absol ignites her fascination, solidifying her resolve to follow him regardless of his objections. Traveling through Hoenn, she observes clashes involving Primal Groudon, Primal Kyogre, and Rayquaza, frequently voicing concern for Alain's safety. Though Alain continually attempts to leave her behind for her protection, her persistence wins out, even leading her to sneak onto Steven Stone's airplane to continue following him. At Lysandre Labs in Kalos, Alain publicly rejects Mairin, declaring her presence hinders his growth. Distraught, she flees, inadvertently leading Chespie into a restricted area where it is exposed to a harmful energy surge while rescuing a Zygarde Core. With Chespie comatose, Mairin remains at the Labs, clinging to hope for its recovery. Lysandre leverages this, promising a cure to secure Alain's cooperation in gathering Mega Evolution energy. Watching the Kalos League finals, Mairin experiences mixed emotions, overjoyed at Alain's victory yet later disillusioned when Lysandre unveils his plan to destroy the world. When Team Flare assaults Lumiose City, Mairin confronts Lysandre about his true intentions regarding Chespie's cure. Rescued from a Team Flare grunt by Professor Sycamore, she joins the mission to retrieve Chespie from Lysandre Labs. Traveling by helicopter alongside Serena, Sycamore, and Team Rocket, she expresses admiration for Serena's battle skills during an aerial skirmish. Her primary Pokémon are Chespin, nicknamed Chespie (which remains outside its Poké Ball, using Vine Whip, Pin Missile, and Toxic), and Flabébé, nicknamed Bébé (captured using Toxic under Alain's guidance, known to use Magical Leaf). Throughout adversity, Mairin's development reveals growing resilience, shifting from naive enthusiasm to determined action during crises. Her relationship with Alain evolves from one-sided pursuit to mutual concern, though his protective secrecy strains their bond. Her unwavering focus remains Chespie's recovery, driving her involvement in pivotal events despite personal risks.