Hapu is a girl that lives on Poni Island, near a field of Poni Radishes that she grows and sells over the island. She learned battle skills with her grandfather
Sofu, who was the former Island King. Although Hapu's parents live in the area as well, they say she refuses to leave the farm as she's attached to it as she used to live there with
Sofu.
She really doesn't like to lose battles. There weren't any children her age living in her neighborhood growing up, so her battle opponents were always adults. While she was younger, she lost a lot, but she kept challenging the adults on the island until she finally started winning.
Someone kept steeling all her precious Poni Radishes and she thought
Ash Ketchum was one of the people stealing them. The radishes from Hapu's farm are especially well-rounded while retaining their spiciness, so they're as delicious as they can be and therefore making them a target for thieves.