Later, she greets the player and Lillie when they arrive at her home on Poni Island, where she lives with her grandmother. She travels with them to the Ruins of Hope in hopes of contacting Tapu Fini. Hapu is then chosen to be the new Island Kahuna by the guardian deity, succeeding her deceased grandfather, and receives a Sparkling Stone as a sign of her new position. Hapu then agrees to tell the player and Lillie all she knows about SolgaleoSUS/LunalaMUM, and directs them to Exeggutor Island to find the remaining flute needed to summon it.
"Well met! I was seeking you. If you're going to travel about Ula'ula, you ought to do it while astride a Mudsdale. There is no call for hesitation. Consider it my thanks for Akala Island."
"It was remiss of me not to register her for you when we met one another in Malie. I was just so taken aback by Lillie and how lovely she was that it escaped me. By no means was I just waiting for a time when you were in trouble!"
"If you seek the next trial, go straight on through here to Tapu Village. I'll be cheering for you on your island challenge!"
"I give my thanks... for your great blessing. As kahuna, I will do my best for the people... and the Pokémon of Alola."
"Oh! So you two were watching?"
"The kahunas are chosen by the Pokémon we worship here in Alola—our sacred guardians. They are chosen from among the people living on the island each guardian watches over. Lillie told me that you're pretty new to our parts, eh, <player>? You came to Alola from far off? You must really be something then. I heard how you were given a sparkling stone by the tapu, even as a stranger to our shores."
"My grandfather... My grandfather was also chosen for this honor. The honor of being our island's kahuna. But he died suddenly some years back, and we were left without a kahuna on Poni."
"I tried to follow in his footsteps, but I was not chosen by the tapu back then. So I set out on my own sort of island challenge, traveling Alola and trying to grow stronger."
"Lillie. The kahuna you wished to meet is right here."
"So you want to know about SolgaleoS/LunalaM, who we pay tribute to at the Altar of the SunneS/Altar of the MooneM?"
"The world of the beasts, eh... Is that what that thing was that came to Poni Island? A beast? Tapu Fini and I tried to fight it, but it nearly did us both in. We did not stand a chance."
"All right. I will tell you what I know."
"But what I know is not much. Just that there is a ceremony held for the Legendary Pokémon at the altar. A ceremony that uses two particularflutes to somehow give the Legendary Pokémon power."
"Ho! That looks to be the flute that used to reside at the lake on Ula'ula."
"The other is said to be held on Exeggutor Island. I do not know why there of all places, but it has been passed down that that's where it belongs."
"Yes. And no reason to dally here. Let us go and speak with the seafolk's chief! Lillie, you take Mudsdale. We proceed to Seafolk Village!"
"Nothing wrong with that. People cannot survive all on their own. They have got to help one another out. Same for Pokémon, too. That is what my grandfather used to say."
"I would like to see this battling skill of yours, <player>, that makes Lillie smile so."
"Just so! It is my grand trial! I may be young, but that does not mean that I will be outdone by any of those other kahunas! I am certain that my bonds with Mudsdale and the rest of my team are the closest you will find anywhere in Alola!"
"Do you want to try to take me and my Pokémon on at our full strength?"
I need to prepare first: "Then I will wait."
Only if you'll take on mine: "Ahaha! Now, don't be hasty, <player>! Look at the state of your Pokémon. We have got to have them in peak condition for this to be a fair fight./I am Kahuna Hapu! And I have made the sparkling stone that the tapu entrusted me with into a Z-Ring of my own!"
"Having a Z-Ring like we do, <player>, means that we battle with the tapu beside us."
"This is the first grand trial of Kahuna Hapu! I will battle you with everything that I have got!"
If talked to again if "I need to prepare first" is chosen or after the player healed their Pokémon
"Come! If you want to proceed to that canyon, you will have to get through me and my grand trial!"
Upon being defeated
"Thud! That's the sound of your strength rocking me to my core!"
After being defeated
"Oho... You sure showed me."
"That was enjoyable. Looks like I cannot beat you even when I am not holding back... I appreciate this chance, <player>. It has really taught me a few things."
"Ah, and here is <player>! A meeting by chance is preordained. We shall dine together! Chief! The usual for me and my friend <player> here."
"And here it is! When I am too busy working our fields to get a proper meal in, I always depend on the good folks here to help keep me fed. You sure end up with a mighty appetite after a pleasant bit of work!"
"Phew... That hits the spot! And with just a little extra space to spare, too. It is not good to overeat, you know. That is why I like the portions here so well. Hm? What is the matter, <player>? Do not tell me that you do not mean to finish? What a waste!"
"I sell them our vegetables wholesale, so they let me eat for free. So let me treat you today. Have these, too."
"Well then. I would say it is time we both got back to work."
In Showdown on Poni Island!, after praying at the Ruins of Hope, Hapu watched as Mudsdale stepped on a Corsola branch, which became lodged in its hoof and caused it to go berserk. Ash and Pikachu were able to dislodge the branch with Iron Tail, which calmed Mudsdale down. As they walked, Ash revealed he wanted to challenge Tapu Fini to a battle for his grand trial. Offended by this, Hapu had Mudsdale kick Ash and send him flying. She continued to chase after Ash before being stopped by Lillie. Hapu later refereed the battle between Ash and Gladion, and then watched as Tapu Fini flew over them.
In SM107, Hapu helped taste-test some of Mallow's daikon-based dishes.
In SM108, Hapu had Ash and the others help out at her daikon farm. When a mist caused by Tapu Fini filled the area, Ash, Mallow, and Lillie went missing. Worried they would be trapped in the mist forever, Hapu traveled to the Ruins of Hope and confronted Tapu Fini in an attempt to stop it. The spirit of Sofū, her deceased grandfather, appeared, revealing that Tapu Fini has accepted Hapu as the next Island Kahuna of Poni Island. After meeting back with the others, Hapu revealed she was made the next Kahuna and promised to have a grand trial with Ash after she properly received the Kahuna title through a ritual.
In SM109, Hapu performed the ritual with Tapu Fini and officially received the title of Island Kahuna. Later, she faced off against Ash in a grand trial, but was defeated. As a reward for his victory, Hapu presented Ash a box of type-specific Z-Crystals and allowed him to choose from one of them as his prize. As gratitude for his hard work, Ash let Pikachu make the choice for him, and he picked the Steelium Z. Later, as Ash and his classmates headed back home to Melemele Island, Hapu gave them some Poni daikon as a parting gift before saying her farewells.
Hapu is a very lonely and reserved individual, choosing to spend her days collecting her daikon due to having nothing better to do. As a result, Hapu is eager to invite others to her house, becomes quite delighted at having guests around in order to alleviate her loneliness, and often releases her Pokémon from their Poké Balls to keep her company. When questioned, however, Hapu is quick to deny being lonely, claiming she feels comfortable being alone even to her own Pokémon.
Hapu speaks in a rather sophisticated manner, using longer and old-fashioned sentences to express herself. She is also quick to judge others, such as when she assumed Ash was the one behind the theft of her daikon, despite having no evidence to support this. Upon being proved wrong, Hapu is also able to easily and quickly recognize her mistakes and apologize.
Being the granddaughter of a former Island Kahuna, Hapu possesses great knowledge behind the concept and true meaning of being a Kahuna, while also showcasing vast knowledge about the myths surrounding Tapu Fini and its abilities. Her knowledge, respect, and dedication to her island's history and tradition caused Tapu Fini to recognize Hapu as being worthy of being named the next Island Kahuna.
Golurk is Hapu's first known Pokémon. It helps Hapu with her farming by picking daikon out of the ground and helps its Trainer get around by flying around the island. When Hapu assumed Ash to be a daikon thief, she used Golurk to battle Ash's Pikachu and won.
Mudsdale is Hapu's second known Pokémon. She uses it to transport daikon by loading them on bags on its side. When confronting Team Skull, she used Mudsdale to battle them and easily won. In SM109, Mudsdale was used in Hapu's Grand Trial against Ash. Despite its strength, Mudsdale was eventually defeated when Pikachu splashed water on it, simulating the effects of Soak, allowing it to defeat it with Gigavolt Havoc.
Hapu's Mudsdale easily defeated the Crabrawler horde, but struggled against the leader Crabominable's ability to accurately hit Mudsdale's weak points even after being blinded. Hapu managed to to seize victory after Sun used MachampShove to sway the boat and move Mudsdale's body out of the way of Crabominable's attack and leaving the Woolly Crab Pokémon defenseless to Mudsdale's next attack. With Crabominable defeated, Sun asked Hapu to deliver the Mirage Berry as he was too injured from earlier to do so. Hapu accepted, but is shocked to receive a Sparkling Stone from Tapu Fini, who was watching the battle the entire time. Overjoyed that the guardian deity accepted her as the next Kahuna of Poni Island, Hapu cried tears of joy.
Afterward, Hapu and Sun traveled to the grave of Hapu's grandfather on Vast Poni Canyon. Hapu wished to meet with her grandfather so that she could show him that she became the next Kahuna of Poni. As they traveled, the Crabominable from before followed them in the hopes of joining Hapu's team. Hapu rejected Crabominable's request and suggested it join Sun's team instead, which it reluctantly agreed to. Hapu then revealed she possessed the Moon Flute and asked Sun if he was capable of playing it. Later, Hapu and Sun witnessed Nebby and another Cosmoem fly to the top of Vast Poni Canyon to meet with each other.
Noticing that the Cosmoem are moving to the Poni Altar, Hapu and Sun decided to postpone their grave visit and follow the two Protostar Pokémon. As they traveled, Hapu told Sun about Solgaleo and Lunala, two Legendary Pokémon that are said to have come to Alola from another world, similar to the Ultra Beasts. She also stated that the Moon Flute is meant to be played with another flute at the Poni Altar. The two are then surrounded by a group of Aether Foundation Employees demanding that Hapu come with them to the Poni Altar. Before the Employees could attack, a Xurkitree lands on top of them, having already been defeated by Gladion, who also asked Hapu about the Poni Altar. After the Employees retreat, Hapu noticed that Lillie is in possession of the missing Sun Flute. While Gladion is unable to play the Sun Flute, Sun is actually able to get it to work. The four guardian deities of Alola then appear and takes Sun to the Poni Altar along with the Sun and Moon Flutes. Hapu, Gladion, and Lillie then proceed to follow after them.
Upon arriving at the Altar and meeting Anabel, Hapu and the others discovered that Sun and Moon managed to evolve Nebby and the other Cosmoem into Lunala and Solgaleo, respectively. Shortly after, Anabel received a call from Looker, who reported that a large number of Ultra Beasts have made their way to Poni Island. Hapu, Moon, Gladion, and Anabel fought off the attacking beasts, but were interrupted when a large Ultra Wormhole opened up with a hand emerging from it. The hand grabbed Solgaleo, taking control of its body. The possessed Solgaleo grabbed Sun with its tail and jumped into the wormhole while Moon and Nebby chased after them.