Kieran is a student of Blueberry Academy native to Kitakami. He and Carmine are chosen to accompany the incoming students from Naranja AcademyS/Uva AcademyV on a cultural tour of the area. Kieran is paired up with the player character, and accompanies them around Kitakami as they search for three signposts that tell the story of how the Loyal Three laid down their lives to protect the land from the evil Ogerpon. During this time, Kieran admits that he actually admires Ogerpon for her strength and independence.
Spoiler warning: this article may contain major plot or ending details.
At the end of the first day in Kitakami, the player, Carmine, and Kieran attend the Festival of Masks. The player and Carmine have a chance encounter with Ogerpon, who flees and drops her Teal Mask. Carmine decides to keep this incident from Kieran, fearing that the knowledge he missed a chance to meet his idol would break his heart. The next day, the player and Carmine learn from the siblings' grandfather that the "Loyal" Three were actually a group of bandits who attacked Ogerpon's Trainer and stole three masks made for her by the siblings' distant ancestor; Ogerpon slew the Lousy Three, but the villagers believed she was attacking them and came to fear her. Unbeknownst to them, Kieran overhears their conversation and concludes that they are excluding him out of contempt. While the player and Carmine search for materials to repair the Teal Mask, Kieran steals the mask, accuses them of treating him like an outcast, and demands the player defeat him in a battle to reclaim the mask.
After the player defeats Kieran, he surrenders the mask as agreed. However, the Lousy Three unexpectedly come back to life and are given food and Ogerpon's stolen masks by the ignorant villagers. While the player, Carmine, and Ogerpon pursue and defeat the Lousy Three, Kieran convinces the villagers that the old legend was mistaken and that Ogerpon was innocent all along. With Ogerpon's reputation rehabilitated, the group returns to Ogerpon's mountain home, where Ogerpon chooses the player to be her Trainer. However, a jealous Kieran demands a final battle with the player for the right to take Ogerpon, irrespective of Ogerpon's wishes. The player defeats Kieran, who watches them catch Ogerpon before fleeing home, locking himself in his room, and refusing to come out or see the player off.
After the end of the tour, Kieran and Carmine are to return early to Blueberry due to an unexpected development in the Great Crater of Paldea. Kieran, now consumed by his resentment towards the player and obsession with strength, vows to become even stronger and ominously declares, "Just you wait" to the player.
When Kieran punches the Loyal Three's shrine after his third battle, a purple mist can be briefly seen in his fist, implying the trio's revival may have something to do with Kieran himself.
↑Carmine says that Kieran is going through "teen angst", implying that he is a teenager;[1] in other languages, Carmine simply attributes his behavior to puberty or adolescence. His actual age is not otherwise known.
↑In the French version of the game, he is explicitly 14 years old.[2]
References
↑Carmine: "What's [Kieran's] problem? He's been all bent out of shape since yesterday. [...] Must be teen angst or something. It happens!" (Pokémon Scarlet and Violet)
↑Roseille: "Kass a quatorze ans, alors il aime bien les créatures qui font peur. C’est aussi pour ça qu’il préfère le Monstre aux Adoramis." (Pokémon Écarlate et Violet)
