A specialist of Poison-type Pokemon, Cain is considered one of the player's rivals, along with Victoria and Fern, and he assists the player and the other protagonists on various occasions in the storyline.
Cain is first met at the Grand Hall, shortly after the player has chosen their starter Pokemon, and he will flirt with the player - regardless of the player's chosen gender - before challenging them to their first battle, after which Cain happily takes it upon himself to show the player around the Grand Hall.
Cain is not encountered again until the player reaches the Coral Ward. Here, Cain arrives just in time to help Amaria save an Oshawott stranded up in the water. Sending his Grimer to safely navigate the poisonous waters (and singing a heroic song all the while), Cain manages to rescue the Oshawott. At first, Cain is content to just head on his way, but when the Oshawott continues to follow him, Cain gives into its adorable appearance and adds it to his team, despite his initial reluctance towards using a Pokemon that is not a Poison-type, and has a battle using it against the player to calm its jitters.
Cain later reveals that he was originally supposed to be the back-up leader for the Venom Badge, but because of his disagreement with his mother over his sexuality, he ran away from home, leaving Aya with this role instead.