I think the movie is a brilliant expression of a person who struggles to survive after a plane crash. The whole plot happens inside his mind in an unconcious stage. The boy survived the terrible accident and lands in somewhere. But his mind is the key that has to keep him away from death. The black spirite that chases is his fear or death. Either he could avoid it or let it take him away. But he tries to stay strong and avoid it untill someone come. He absorbes the nature around him and interprets it as his inspiration. His deep mind imagines that he has to run away from the fear and he does. The black fear was created by the deaths he has seen lively, they all have shown same in shape. As a results of his strong mind set, he survives at the end.
The missing part of the movie is the physics in animation. When the boy jumps into water, startle or fall, I couldn't feel the energy in it. The motion details should have given to embed the feelings strongly in minds. It would be a master piece if that part was fulfilled. For the regular movie seekers, I am sorry, It is not recommended. Its something exceptional.