Throughout the game, you’ll have heard about the guardian deities–the tapu–that reside in the various ruins, and of course you also ran into one of them yourself: . Now that you’re the strongest Pokémon trainer in Alola, the four tapu will finally deem you worthy of gazing upon their presence.
Which translates to: you can catch them! For reference, the four tapu are classified as Legendary Pokémon, although they’re not on the same level as the likes of , and . Even still, they’re a lot stronger than most other Pokémon–and highly recommended to have in a team.