I've been to Ryonaket severaltimes while I was living in Japan. It's amazing! A room full of dozens of booths selling ryona and guro doujin and hundreds of ryona/guro fans to hang out with. I's really fun and I always end up leaving with a heavy backpack full of new books and CDs. If you have a chance to go, you should definitely attend. You won't regret it. Just bring lots of money. Onaverage I spent around 20,000 every time I went because there was so much stuff I wanted to buy. :-)