Tapu Koko is observant, helpful, playful and a good judge of character. Tapu Koko always been observing the people of Melemele Island or Ash from a distance. Sensing Ash's good nature and courage it even trusted Ash with a Z-Ring and even tests Ash's growth as a Z-Ring user.
It also has a mischievous side as the Z-Ring it gave to Ash was originally Kahuna Hala's proving that it also likes to take things even to get others attention. When it took Ash's hat to lure him away so they could battle.
Tapu Koko also appears to not tolerate any impulsive behavior from other people. For example, when Gladion arrogantly yelled at the Tapu Guardians out of impatience, it gave him an angry stare.
Tapu Koko has been watching Ash in amazement from the beginning he arrived to Alola region. It gives Ash a Z-Ring for good purpose. 
It later appeared in front of Ash and his new classmates and teacher and then took his hat to have him follow it. After getting his hat back, Ash discovers that Tapu Koko stops in the middle of the woods to battle and test him to know is he able to use it; Z-Move: Gigavolt Havoc. After Ash was able to used the Z-Move, Tapu Koko congratulated Ash for his success before it flies off into the sky.
It's revealed from Hala that Tapu Koko took the Z-Ring from his house is the same one it gave to Ash. It was also seen observing Ash and his Pokémon completing the Verdant Cavern Trial before flying away.
Then Tapu Koko appears again watching Hala and Ash's Grand Trial battle from afar. When it saw that Ash had won just about as he was about receive the Fightinium Z crystal they all heard Tapu Koko's voice and by their surprise it switched the Fightinium Z for the Electrium Z crystal.
Tapu Koko appears to be watching over the city until it sensed an explosion coming from Sophocles's house, then during the school day. It came to have another battle with Pikachu and during the battle the two used the Z-Move, Gigavolt Havoc and this time the force of it was enough to push Tapu Koko back. But, the battle was over when the collision between the two electric types sent Pikachu flying over the a edge with Ash falling after him. They were both saved by Tapu Koko in which they gave their thanks before it flew away, promising to battle with them again.
Tapu Koko reappeared at the Altar of the Sunne on Poni Island with Tapu Lele, Tapu Bulu, and Tapu Fini. It revealed to Ash and the gang that they were the ones who brought Nebby to Melemele Island where Ash can find it and take care of it. After Ash told them about Nebby's motionless evolved form, Tapu Fini and Tapu Lele perform a ritual around Nebby. But Gladion grew impatient and impulsively yelled at the Tapu Guardians to hurry up so he can rescue Lusamine as soon as possible. Gladion's behavior angered Tapu Koko and gave him an angry glare, telling him to wait longer. With the ritual complete, the Altar of the Sunne activated itself and Nebby evolved into Solgaleo. The Tapu Guardians then gave Ash the Solganium Z, but the only problem is that it won't fit on his Z-Ring. Tapu Koko resolves the problem as it takes the Z-Ring, and through a special dance, it and the other Tapu Guardians upgraded it into a Z-Power Ring. It then watched as Ash and Nebby performed the Z-Move, Searing Sunraze Smash, and enter the Ultra Wormhole to rescue Lusamine from Ultra Deep Sea. After that, the Tapu Guardians went back to their respective islands.
Tapu Koko later appeared where it witnessed Sophocles discovering Celesteela buried in Bamboo Hill and later watching it blast off to the moon. It also appeared where it witnessed the Ultra Guardians bring Blacephalon and Xurkitree back to Ultra Space through the Ultra Wormhole.
During the Alola crisis, Tapu Koko quickly intervened in the fight between Lunala and Necrozma, protecting Lunala from being absorbed by Necrozma, and hitting the Prism Pokémon with Dazzling Gleam. Later, it watched Hala from a distance as he observes the sunrise during the Manalo Festival. Tapu Koko later interfered helped Professor Kukui and Faba attack Team Rocket's ship and prevented them from entering the Ultra Wormhole to capture Lunala, Nebby, and Necrozma. It later helped join everyone in sharing its light to restore Necrozma's original Ultra form. After the crisis ended, it then Necrozma appearing in the skies above Alola before dispersing into light.
Sometime later, Tapu Koko approached Ash and the two started to battle. However, after a clashed between them as it opened up a portal thus sending Ash and Pikachu to an alternate world of Alola region in ruins, Tapu Koko calmly awaited for their return. Once they did, it congratulated them and flew off into the forest.
Tapu Koko later appeared in the Forest Pokémon Café and tasked Mallow, who was assisting Oranguru, in providing a special meal for it. Mallow complied to the task and prepared a burger made out of daikon radish from Poni Island. Tapu Koko was satisfied with its meal and rewarded Mallow the Grassium Z while Oranguru rewarded her a Z-Ring.
Tapu Koko appeared with its other Tapu Guardians to assist everyone in defending the Alola League from Guzzlord and its two shiny cronies. Shortly after defeating the wicked Ultra Beast, Tapu Koko decided to stick around when it heard that Ash was battling that next day against Professor Kukui in a exhibition battle while the other Tapu Guardians went back to their respective islands. While watching the battle and due to the battle being a full six on six, Tapu Koko became impressed with both Ash and his Pokémon growth  Seeing that the Professor Kukui was down to his last Pokémon, Tapu Koko flies down as it not only takes over as the latter final Pokémon in order to battle Ash once again but to also see his growth for itself. It went up against Ash's Naganadel and defeated it immensely. But during its final battle with Pikachu, Tapu Koko and the other Tapu Guardians restored Ash and Kukui's Z-Rings and entrusted the latter with the Tapunium Z. Together, they both performed a powerful legendary Z-Move, Guardian of Alola. But Ash countered it with the 10,000,000 Volt Thunderbolt Z-Move and defeated Tapu Koko. After the battle, Tapu Koko was healed by Tapu Lele and thanked by Kukui for the amazing battle.
- ^ SM001: Alola to New Adventure!
- ^ SM002: The Guardian's Challenge!
- ^ SM009: To Top a Totem!
- ^ SM010: Trial and Tribulation!
- ^ SM019: A Guardian Rematch!
- ^ SM044: A Dream Encounter!
- ^ SM050: Faba's Revenge!
- ^ SM051: Family Determination!
- ^ SM052: Revealing the Stuff of Legend!
- ^ SM069: Rise and Shine, Starship!
- ^ SM078: Twirling with a Bang!
- ^ SM088: Full Moon and Many Arms!
- ^ SM090: Securing the Future!
- ^ SM100: Battling the Beast Within!
- ^ SM101: Parallel Friendships!
- ^ SM121: A Recipe for Success!
- ^ SM140: Z-Move Showdown!
- ^ SM141: Exhibition Unmasked!
- ^ SM142: A Full Battle Bounty!
- ^ SM143: Fiery Surprises!
- ^ SM144: From Z to Shining Z!