Sin-bound Haibane usually feel guilty about something they have done in their previous life and, until they can overcome this, they cannot become a normal Haibane. 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. Rakka is helped by a bird whom she believes to represent someone she knew in her previous life. The idea behind the Sin-Bound is that no one can forgive themselves for their past transgressions; they must learn to be forgiven by another.