Haru is a resident of Akala Island and a frequent customer of Kiawe, who has the job of delivering milk to the people of Alola. He was awaiting Kiawe's fresh delivery of Moomoo Milk to make a birthday cake for his mother. On their way to delivering the milk to Haru however, Satoshi and Kiawe were delayed by Team Skull Grunts. After defeating them, they arrived too late to deliver the milk, but Haru accepted their apology if they promised to show Haru a Pokémon battle. Satoshi and Kiawe agreed to this, and showed Haru and his parents a battle with Satoshi's Pikachu battling Kiawe's Turtonator, after Haru managed to bake his mother's birthday cake and presented it to her.

(Source: Bulbapedia)