The Guardian's Challenge!

On Ash's first day at Pokémon school, Professor Kukui and the other students host a surprise welcome party for him. Soon after Tapu Koko approaches Ash in order to battle Pikachu. Tapu Koko teaches Ash how to use the Z-Ring. Ash and Pikachu manage to unleash the Z-Move, Gigavolt Havoc, but the Z-Crystal shatters after Pikachu's immense release of power. In order to regain the power of Z-Moves, Ash decides to go through the island trials.