We are Kamehamaha. The player is going on King Kamehameha's quest.

From the leak:
>There will be no gyms.
>Alola region has no leagues. Your main objective is to build a league. After you finish building a league, the Elite 4 will appear. The E4 will be like the owners of each island.

King Kamehameha went on a warrior's quest to conquer and unite all the Hawaiian Islands into one country.

Each Alola island has a leader and a guardian Pokemon. They're gonna have us battle them to unite the islands into a Pokemon league! Then, later, it becomes the E4.