Friendship is a theme in "The Absolution True Diary of A Part-Time Indian" because Arnold and Rowdy were best friends for their whole lives until Arnold goes to Reardan, then Rowdy gets mad at him for going there and doesn't speak to him for a long time. After the second basketball game between Arnold and Rowdy's schools, Rowdy decides to pay Arnold a visit and play some basketball with him. They become friends again and play basketball throughout the whole night and didn't want to stop playing at all.
Fitting in is a theme because when Arnold first goes to Reardan, he knew absolutely no one and people kept making fun of him for being Indian. He eventually starts to make friends after he punched Roger in the face (weird way to make friends), he also gets a girlfriend who is bulimic. His tribe on the reservation hates him with a passion for leaving them.
Arnold eventually got what he wanted in his life. He also made a lot of friends in his time at Reardan.