Walkthrough: After reaching Iki Town for the festival, you will quickly be prompted to once again Battle your rival Hau, but this Time to honor Tapu Koko. He has added a New Pokemon to his team, as well as leveling up his Starter Pokemon. After defeating him, Kahuna Hala will give you the Z-Ring that he made from your Sparkling Stone.
Trainers:
Hau (Rowlet Starter) - Level 6 Pichu, Level 7 Popplio
Hau (Litten Starter) - Level 6 Pichu, Level 7 Rowlet
Hau (Popplio Starter) - Level 6 Pichu, Level 7 Rowlet