After exploring areas of Melemele Island that you couldn't reach, you go to the Marina to sail to Akala Island.
Arrival in Heahea City
At the Marina, you will be asked if you are ready to go to the next island. If you are, say yes, and there will be a cut scene as you go to Akala Island.
When you arrive, you meet Kahuna Olivia and Captain Mallow. Professor Kukui says that if you are ready for the first of Akala Island's three trials, go to Route 4 to reach Paniola Town.
In the nearby Ferry Terminal, you can get Fresh Water from the vending machine. You can talk to the girl behind the counter if you want to go back to Hau'oli City.
Farther down the street, there is an Alola Tourist Bureau. The Name Rater is inside. Talk to him if you want to change the nicknames of your pokémon.
If you go farther down the street, you find Lillie. She mentions the Ruins of Life, and Akala's guardian, Tapu Lele. The asks if you will join her when she goes to the ruins, and says she will be in the Tide Song Hotel.
Afterward, you can go into the apparel shop. Talk to the old man and he will ask if you will do a task for him. He mentions Hano Grand Resort, and the pokémon Pyukumuku that can be found there. He asks you to catch one then show him your Pokédex to get a reward.
Outside, go across the street from the apparel store and talk to the woman to get a Rare Candy.
Go a little farther down the street and you will find a Pokémon Center to the right. After visiting the Pokémon Center, go outside and go upward toward the hotel where Lillie went. Keep going toward the hotel until two people stop you. Dexio challenges you to a battle. Pokémon Trainer Dexio has a level 15 Slowpoke and a level 16 Espeon. You get 2240 Pokédollars for winning.
Afterward, Dexio heals your pokémon and gives you the Zygarde Cube. Dexio will explain the details of this item later. As you explore different areas, you might see sparkles. Check on them to absorb them into the Zygarde Cube. If you have a Zygarde in your party, and if you have collected any pink sparkles (Cores) you can go into your Bag, select the Zygarde Cube, choose Use this Item, and use it on Zygarde to teach it a move.
Go upward and go into the hotel. There is a sparkle in the upper-left corner. Check on it to absorb a creature into the Zygarde Cube.
Then when you are ready, go south from the hotel, then east to enter Route 4.