Pop into any bookstore and you'll find shelves overflowing with comic books about samurai, yakuza, war, business, baseball, soccer, golf, examination hell, high-school romance, office affairs -- in every genre from sci-fi to porn. And that's just the tip of Japan's manga iceberg.

But one thing you're not likely to find there are dojinshi -- underground comics read by hundreds of thousands every week that make even the most off-the-wall mainstream manga look simply mundane.

Dojinshi, meaning "niche journal," doesn't refer to any one style of publication, but to a way of publishing. Unlike their mass-market counterparts, stamped with ISBN numbers and sold at licensed bookstores, these underground manga are run off in small batches by amateurs who mainly sell them by mail order, through specialist shops or at comic-book conventions.