If May is selected as the player character, she starts her journey moving from her home in Johto to her new home in the town of Littleroot in Hoenn. After saving Professor Birch from a wild Pokémon, she is given one of the three starters of the Hoenn region. May develops a close bond with Brendan, and eventually Wally, who both act as her rivals. May goes on to gather the eight Badges of Hoenn, stop the plans of Team AquaSEAS/Team MagmaREOR and conquer the Pokémon League all before going off to face the Battle FrontierE/Battle MaisonORAS.
As a non-playable character
If May is not selected as the player, she is helping her dad finish the Hoenn Pokédex and becoming a Pokémon Professor. She is also the player's rival and friend. Along with Brendan (when playing as May), they are the only rivals unavailable for battle after entering the Hall of Fame. Additionally, they both are the only ones to not evolve their starter Pokémon into its final form, except for in Omega Ruby and Alpha Sapphire, where their starters have been fully evolved by the battle that takes place after the credits.
If the player never uses the Rustburo City PokéCenter and blacks out during a wild Pokémon encounter after rescuing Peeko, they will encounter May on Route 104 when going to Mr. Briney's home.