On paper, it sounds like a potential classic: the tale of adolescents at the mercy of adolescent pack mentality, who turn to a glossy, mysterious chanteuse for spiritual solace - and to one another, in fans-only chatrooms, for more immediate companionship. It promises much: the vivid microcosm that is Japanese pop culture, the universal resonance of classroom cruelty, an iconic singer who pays homage to Debussy, and maybe even some great music too.

With such promising seeds, it's hard to explain why All About Lily Chou-Chou doesn't quite work; and harder to disentangle the bitterness, isolation and basic lostness the film intentionally conveys from the isolation and lostness the viewer ends up feeling by trying to follow it. It's a dark piece of storytelling - so much so that the darkness obscures much of the narrative, and we're left as frustrated and confused as the schoolboy Yuichi.

The film traces episodes in Yuichi's life as his former best friend Hoshimo breaks away from his academic reputation to terrorise his fellow students - Yuichi now included amongst them. Essentially a passive character, Yuichi serves as a kind of go-between; he is both keeper and silent guardian angel to a girl Hoshimo forces to prostitute herself, silently distressed but never stepping in. The only place he expresses his unhappiness and anger is (guess) on the Lily fan site he runs for like minds. Otherwise we see brief, bleak flashes from his school and home lives as he and other students operate under a monochrome victim mentality.

In this context, it's actually the isolated bits of symbolism that work best: in one scene late in the film, two red kites trace the same path through an afternoon sky, one following the other precisely. This one delicate image expresses much more about the fickle emotional life of the characters than the comparative crudeness of their onscreen interactions, which soon branch out from petty theft into near-death experiences and sexual violence. One of the most unsettling features of the film is the way that the angsty, pseudo-mystical exchanges between the chatroom fans do actually translate into real-life tragedy; it lends a potency to feelings that by late adolescence most of us have already learned to laugh at.

As a film-going experience, there are some very powerful images and ideas buried in Lily Chou-Chou; unfortunately, it becomes harder and harder to access them through the frustration of a film that is much too long, much too disconnected and almost entirely uncommunicative about the points it sometimes succeeds in making, sometimes doesn't. The ambiguous timeline also muddies the narrative waters to the extent that halfway through the film our entire party lost the plot and disengaged from it somewhat. It's good to see the role of internet communities given a thoughtful examination, a treatment that at least suggests the stimulation and last-resort emotional support they can provide, but perhaps the way to treat a pixellated, soundbitey popular culture is not to embed it in a grand narrative.