I think that the theme of the book is that: It takes time to figure out how you define yourself.
I think this because during the whole book, it is showing the different moods and characteristics the different characters show. Their feelings and the way they act keeps on changing throughout the variety of events that occur. For example, on page 83, it talks about how Luka "found" Karara, and so is trying to get her into trouble. Now Luka was angry at his sister, and so shows he has a dark side. Though on page 43, Luka is scared and sorry for Karara, because maha is whacking her with a bamboo stick. These are two different feelings from Luka. Pages 8 and 9 talk about Tirios first lesson with Wata. How Wata picked out a pierid butterfly from it's group, plucked of a wing and waited till a horned frog came and ate it. Connecting to this, on page 133 and 134, Tirio by accidentally steps on a colony of bu-ki ants. After he notices that he stepped on them, he feels sorry for the ants. One of the ants was limping afterwards. He says to himself: "I'd forgotten how cruel nature is."