Dr. Kukui is a Pokémon researcher from Alola who's basically obsessed with understanding how moves work. He's best known for his willingness to take direct hits from Pokémon attacks if he thinks it'll help him learn something—which tells you pretty much everything you need to know about his dedication (or lack of self-preservation instinct). He lives in the player's new hometown and comes across as genuinely passionate about his work.
Early on, he teams up with Hala to hand out starter Pokémon to both the player and Hau. Lillie works as his assistant, though she's got her own reasons for being around.
Content compiled by AnimeList.moe from publicly available sources.
