I just noticed... Theodore's branch has the form of a crown of thorns, which I think alludes to the suffering he has inside, i know there are other things you could infer from this allegory, but I think in this case his personal suffering imposed by others is the strongest one.
Second-to-last page: as if his other crimes aren't enough, Akira is also littering.
What a fucker, ain't he? He already dirties the world with his mere presence
(and doesn't have the consideration of disposing of himself for that), but he even has the rudeness of littering.