May is a young Coordinator who loves shopping and eating treats. She has a particular fondness for food, especially noodles. When someone steals her food, she gets angered, to the point of yelling at people. May is generally very sweet and optimistic, though she shows a tougher side sometimes, such as when she argues with her little brother, Max. Even though they argue often, she has shown that she deeply cares for her brother.
She sometimes takes an interest in helping other people with their romantic problems. She loves making her own Pokéblocks with recipes that she thinks up, including ones called "May's Purple Surprise" and "May's Pink Surprise" (Japanese: Haruka's Delicious and Haruka's Delicious 2). The only ones who liked her Purple Surprise were her Munchlax and Jessie. "May's Pink Surprise" came from the recipe for food Professor Oak uses to feed Ash's Snorlax. Thus, after May first fed it to her Munchlax, it was automatically made full. This was subsequently used to feed Munchlax to prevent it from eating the food of others.
It was revealed by Max in A Cacturne for the Worse that as a small child, May was afraid of Pokémon. There was one instance in particular that truly embarrassed May. One day she was swimming in the ocean and was suddenly surrounded by a school of Tentacool. May got scared and called to her parents. She was wearing a blue swimsuit and a matching blue swimmer's cap, leading her mother to believe she was actually a Tentacool. Her mother tried to catch her with one of her Poké Balls. One of May's opponents in a contest recorded Max telling him this to embarrass May into losing.
When May debuted in the anime, she did not like Pokémon at all and was only interested in becoming a Pokémon Trainer so she could travel. Everyone expected her to become a Trainer, to follow in her Gym Leader father's footsteps. However, after seeing a Contest in All Things Bright and Beautifly!, she decided to become a Pokémon Coordinator. Though she was initially shown to not know much about Pokémon or attacks, she gradually gained experience through her journey and soon became a talented coordinator, with her skill being displayed in her Grand Festival rankings in the Hoenn and Kanto regions. Dawn once referred to her as the "Princess of Hoenn" when they met.
As a Coordinator, May was able to learn more about Pokémon. For her Contests, she was able to come up with different attack combinations. She was able to use these combinations in battle. An example of this would be using her Combusken's Fire Spin and her Squirtle's Bubble to create a combination of fire and water, dubbed Fire and Water Whirlwind by Lilian. This even got a rival of hers mad, thinking she thought he was not worthy of the move so May did not use it against him.
During her journey, she finds a rival in Drew, a skilled and sometimes arrogant Coordinator who was one of her main inspirations to try harder to further her skills. Another rival of hers, Harley, is a flamboyant man who goes to extremes to beat May. At the Kanto Grand Festival, May competed against Solidad, an experienced Coordinator to whom she lost to in the semi-finals. At the end of the Advanced Generation series, she left to compete with Drew, Harley and Solidad in the Johto region, aiming to find her own style. May has Contest Passes to compete in Hoenn, Kanto and Johto.
May reappeared from Our Cup Runneth Over! to Strategy With a Smile! to participate in the Wallace Cup alongside Ash, Dawn and Zoey. During this period, she wore the Emerald Version of her outfit. May made it all the way to the finals of the Wallace Cup, but narrowly lost to Dawn in the end.
May has a personal ending theme song, I Won't Lose! ~Haruka's Theme~, performed by KAORI. It was first used as background music in the episode Curbing the Crimson Tide and again in next episode, What I Did for Love. The theme was also used in the Appeals Round at the Wallace Cup for May's performance.