They are also referred to as the tapu (Japanese: カプkapu), the guardians (Japanese: 守り神guardian deity), the sacred guardians (Japanese: 守り神guardian deity), the island guardians (Japanese: 島の守り神island's guardian deity), the spirit guardians (Japanese: 守り神guardian deity), the land spirits (Japanese: とちがみポケモンLand Spirit Pokémon), or the guardian tapu (Japanese: 島の守り神 カプisland's guardian deity kapu). They share the signature move Nature's Madness and its corresponding Z-MoveGuardian of Alola.
According to the legends of Alola, the Guardian deities serve as protectors of the island each resides in. At one point, they participated in war against each other. Eventually, due to the destruction the war brought, they stopped being involved in human affairs. They occasionally fight to see who is the strongest, which lead to the creation of the Battle Royal format. Whenever an Ultra Beast appears in Alola, the deities will fiercely fight against it in order to protect their islands from invaders.
According to secret notes found in the Malie Library, Necrozma, the "Pillager of Light", once invaded Alola, stealing all of its light and shrouding the region in darkness. The Guardian deities fought to regain back the light stolen. Together with the assistance of a youth and the power of Z-Crystals, the Guardian deities banished Necrozma from Alola, restoring its light and freeing SolgaleoUS/LunalaUM.
Among the guardian deities, Tapu Koko plays the largest role within the games' storyline, appearing before the player picks their starter Pokémon to save them after they fall from a broken bridge with Nebby in tow. Tapu Koko, in recognition of the player's bravery, gives the player a Sparkling Stone, which is later refined by Hala into a Z-Ring. Tapu Koko later appears to defend Melemele Island against the then-unidentified Ultra BeastBuzzwoleS/PheromosaM alongside Hala. After becoming Champion, the player and Lillie visit Tapu Koko at the Ruins of Conflict to give thanks to it, after which the player battles it. After catching or defeating it, the player receives the Tapunium Z.
Tapu Fini, while not physically seen, plays a small role in the story as well, granting Hapu the title of Island Kahuna after her grandfather, the previous Kahuna, passed away.
The player can battle and catch the other guardian deities after the credits roll.
Pokémon Ultra Sun and Moon
The guardian deities play a near-identical role in Pokémon Ultra Sun and Moon as in Pokémon Sun and Moon. However, instead of defending against Buzzwole or Pheromosa, Tapu Koko comes to battle BlacephalonUS/StakatakaUM. Additionally, Tapu Koko is not battled during the credits sequence. All four guardian deities can be approached in their respective ruins after the credits. After catching or defeating their first deity, the player receives the Tapunium Z.
In the anime
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Tapu Lele first appeared in True Identity and the Totem Pokémon of Brooklet Hill, where it fought against a Xurkitree that tried to escape from an Ultra Wormhole and lost. It was saved by Moon, who fired a Poké Ball-tipped arrow at Xurkitree, forcing it to retreat back to where it came from. Afterward, it returned to the Ruins of Life to recuperate, only for Gladion to arrive and try to capture it. After being defeated by Sun, Gladion gave up on Tapu Lele, claiming that it was too weak to fight against the Ultra Beasts. Once Gladion left, Sun successfully delivered the Mirage Berry to Tapu Lele. As thanks, Tapu Lele decided to test the abilities of Sun and his friends by battling them. Though it proved to be powerful, Tapu Lele left satisfied after Sun managed to land a hit on it with his newly-evolvedTorracat, Dollar.
Tapu Bulu first appeared at Po Town, where it rescued Sun, Moon, and Anabel from an attacking Blacephalon. Sun was initially reluctant to give a Mirage Berry to Tapu Bulu, as he felt that it had no reason to help humans as one was responsible for the appearance of Ultra Beasts in Alola to begin with. Moon argued that if humans were the cause, then they should take responsibility by fixing the mess as well. Sun and Moon then give the Mirage Berry to Tapu Bulu, which it readily accepts.
Tapu Fini first appeared at Seafolk Village, where it watched Hapu battle a group of wild Crabrawler led by a Crabominable. Tapu Fini watched the battle to see if Hapu was worthy of succeeding the title of Kahuna of Poni Island. After Hapu successfully defeated the wild Pokémon, Sun had her deliver the Mirage Berry, as he was too injured by Crabominable's attacks to do so himself. Hapu then received a Sparklng Stone from Tapu Fini, confirming that it accepted her as the next Kahuna.
The guardian deities are the only Pokémon to have an interpunct in their Japanese names.
Each guardian deity is the same color as the island they represent. For example, Tapu Koko is yellow, whilst "Melemele" is Hawaiian for yellow.