They call it ''Yaoi'. The derivation of the word is obscure. Some think it's just the Japanese way of saying 'gay'. Others claim the word is an acronym, derived from: 'yama nashi, ochi nashi, imi nashi' (which loosely translates as 'no story, just the good bits').

Whatever the etymology, the meaning is clear. Yaoi is the name of a bizarre sex phenomenon sweeping Asia: girls who are devoted to comics and pornography which focus on love, sex and romance - between men.

Of course, it's well known that men like the idea of sex between women. Lesbian erotica - for men - is arguably the most popular genre in the porn industry. But hitherto it was generally presumed that women were not interested in boys getting hot with other boys. The craze for Yaoi suggests this isn't true.

Yaoi began with Manga comics called shonen-ai, which depict, in a rather softcore way, intimacy between young men and originally aimed at gay men. But then the Japanese publishers noticed that many of their readers were heterosexual - and female.

Since then Yaoi, also known as BL (for Boy Love), has developed as a genre: with stories, comics and pornography specifically marketed at girls. Commonly these books and movies are written, shot and devised by women artists.

The stories have a formula. They usually feature a dominant male character - tall and masculine - who deflowers a smaller, more androgynous teen. Sometimes the stories are seriously explicit; these comics also attract a gay male readership, a rich irony.

What do girls see in Yaoi? Theories range from the obvious - "it's