I watched this film on DVD for a second time tonight and I am sitting here struggling to comprehend the underlying meaning. I guess that begs the question as to whether there actually is one! Well, according to the director he wants to express the irrational. But is this irrationality based on some real underlying disturbance? I personally saw reflections of a number of underlying themes and I am wondering whether anybody else felt the same way. It seemed to me in particular that there was an element of repressed anger and violence in the Japanese society, as is so evident in Japanese anime (especially the 'hentai' variety). It certainly was a powerful film and the self destructiveness and brooding anger of the three central characters was certainly frightening yet moving at the same time.
I still wonder what the ending meant though, but I am tempted to interpret the parallel between the lead characters as an expression of some sort of common pent up repression of Japanese society. Let me know lest I start punching walls or succumb to the compulsion to have my head pounded :-)