Marin is a young Pokémon trainer with spiky maroon hair, orange eyes, and fair skin. Her attire includes a yellow long-sleeved shirt, a light green cloak featuring darker edges, long dark green pants with light green accents, brown suspenders, gray socks, and brown shoes. She accessorizes with an orange-yellow scarf, a small bracelet, and a green hat adorned with orange triangles and a yellow pompom. Adventurous and persistently cheerful, Marin frequently attempts to uplift Alain's spirits despite his dismissive reactions. She displays occasional confusion, such as misunderstanding whether she or her Pokémon would undergo Mega Evolution. When Alain explicitly calls her a burden, she experiences deep sadness, particularly after her partner Chespin falls ill from exposure to a mysterious green light. Marin demonstrates fierce loyalty by risking her safety to protect Alain during conflicts with Legendary Pokémon and remaining devoted to Chespin during its coma. She began her journey after receiving Chespin as her starter Pokémon. Marin first encountered Alain while observing his battle against a Mega Absol, inspiring her to follow him to learn about Mega Evolution. Despite Alain's requests for solitude, she insisted on accompanying him. During their travels, she captured a Flabébé with Alain's guidance but felt abandoned when he left to battle Siebold of the Kalos Elite Four without her. In Hoenn, Marin witnessed Alain's battle against Champion Steven Stone and the subsequent emergence of Mega Rayquaza, which destroyed ancient ruins containing a giant megalith. Alain protected her from falling debris during this event, sustaining an injury. She later expressed fear during clashes between Primal Groudon and Primal Kyogre, sneaking onto Steven Stone's aircraft to stay near Alain despite her anxiety. When Alain was knocked unconscious in the battle, she rushed to his aid with Steven's Metagross. After returning to Kalos, Alain abandoned Marin at the Devon Corporation to protect her, but she pursued him with Steven's assistance. At Lysandre Labs, she cheered for Alain during his battles against multiple Mega Evolution trainers. Alain publicly rejected her companionship, claiming she hindered his strength, which devastated her. Shortly afterward, Chespin collapsed with a green glow and entered a comatose state. Marin stayed at its bedside in Lysandre Labs, distraught and pleading with Lysandre for help. During the Kalos League finals, Marin supported Alain from the stands, noting his rare smiles during the battle and crying tears of joy at his victory. She later questioned Lysandre's motives after he announced his plan to destroy the world. When a Team Flare grunt attempted to capture her, Professor Sycamore and his Garchomp intervened. She then accompanied Sycamore and Serena to retrieve Chespin from Lysandre Labs, expressing admiration for Serena's battle skills during a helicopter escape from Team Flare agents. Throughout her journey, Marin's bond with Chespin remained central to her character, driving her actions during its illness and recovery. Her experiences with Alain evolved from admiration to heartbreak, ultimately strengthening her resolve to protect others amid Team Flare's uprising.