Complex sentence: The theory that Haibane, in general, are reincarnations of humans in a previous life is supported by clues in Reki's dream--in her dream, Reki steps in front of a moving train and presumably kills herself.
Split into simpler sentences: The theory that Haibane, in general, are reincarnations of humans in a previous life is supported by clues in Reki's dream. In her dream, Reki steps in front of a moving train and presumably kills herself.