We have four guardian deities guarding the four islands in Pokemon Sun and Moon. Tapu Koko, the first you can catch, rests on the Melemele Island. Tapu Lele guards Akala Island while Tapu Fini guards Poni Island and Tapu Balu Ula'Ula Island. They are legendaries, but they can be caught.
First things first, you have to be an Alola champion before you can catch any of these four. If you have already achieved the prestigious title just days after the release of Pokemon Sun and Moon, then read on to get your legendaries.
How To Catch Tapu Koko
Once you become the Alola champion, the character Lillie will push you towards the Ruins of Conflict. Touching it will challenge Tapu Koko at level 60, the guardian deity of Melemele Island. When you successfully Tapu Koko, you will obtain the legendary Pokemon at level 60. The following moves will also come with it: Nature's Madness, Discharge, Agility and Electro Ball.
How To Catch Tapu Lele
When you get the chance to catch Tapu Lele, the guardian deity of Akala Island, by becoming an Alola champion, head over to the Ruins of Life to challenge it. To do so, touch the pedestal at the end of the ruins. Note that you need to have the Machamp Poke Ride. Upon successfully catching it, a level 60 Tapu Lele will come into your possessions. The follow abilities will also come with it: Nature's Madness, Extrasensory, Flatter and Moonblast.
How To Catch Tapu Fini
Tapu Fini, the guardian deity of Poni Island, can be challenged when you go to the Ruins of Hope. Simply touch the statue at the end for it to appear at level 60. You will need Machamp again for this. You will get a level 60 Tapu Fini when you capture it.
How To Catch Tapu Bulu
You can challenge Tapu Bulu, the guardian deity of Ula'ula Island by going to Ruins of Abundance. As usual, you will have to touch the statue at the end. This location is not something you will naturally encounter as you progress through the story, so you will have to go out of your way.
Tapu Bulu is located in the Haina dessert. There are specific directions you must follow to get to the ruins: Up, Right, Up, Right, Left, Down, Up, according to BGR. You can go to Route 13 then go north. Then a level 60 Tapu Bulu will appear after you interact with the statue.
It is advised that you bring as many balls as you can when attempting to catch one of these guardian deities. They are legendary Pokemon, so they are understandably hard to catch. If you accidentally defeat them in battle, try if you can challenge them again by leaving the island then going back to their statues.
If not, some players have suggested that you have to defeat the Elite Four again. Let me know in the comments below if you were able to challenge them again just by leaving the island.
If you liked this Pokemon Sun and Moon guide, check out the others: How to Hatch Eggs Faster; How to Get a Female Salandit; Team Skull's Passwords; How to Get a Shiny Pokemon; and How to Transfer Pokemon from past titles.