The narrator's character traits/character development
The narrator was determined, an example is when he refused to accept Doodle would never walk. He took him to Old Woman's Swamp to practice standing every day. Eventually, after weeks he stood and later he could walk. Looking back he thought” “It seemed so hopeless from the beginning that it's a miracle I didn't give up.” (page 4) This is an example of indirect characterization because his determination was inferred based on the character’s thought.
"I would teach him to run, to swim, to climb trees, and to fight...we set the deadline for...less than a year away." (page 6) This shows that the narrator was ambitious because he was successful in teaching his brother to walk so he set the bar much higher with his expectations. This is indirect characterization because we are inferring the narrator is ambitious based on his actions. The scene above is the narrator having Doodle practice rowing.
Though the narrator could be cruel at times he loved his brother. This is blatantly clear when he finds his brother dead and he throws himself on him. He said, "for a long time, it seemed forever, I lay there crying, sheltering my fallen scarlet ibis from the heresy of rain" (page 10). It is an example of indirect characterization because you infer the narrator cares for his brother from his actions.