>>55605086??? -> Cheren wants to be strong
??? -> Cheren changes his philosophy
A Kahuna is Hau's grandfather -> Hau has an inferiority complex
Hau has an inferiority complex -> Hau prefers not taking battles seriously
Hau prefers not taking battles seriously -> Lillie gets kidnapped
Lillie gets kidnapped -> Hau wants to become strong more seriously to prevent something like that from happening again
Hau's character changes because of "but and therefore" storytelling. The way his character changes makes sense as direct consequences of events in the story.
Cheren's character changes because of "and then" storytelling. His character changes because it just does. There's no logical reason for him obsessing over being strong and then there's no logical reason for him randomly deciding to change his life philosophy. He just does because the game wants to force a character arc because character arcs are inherently good, right?