The new law specifically bars only the sale to minors of the restricted comics and videos. But industry executives say it will essentially end publication of the material by discouraging risk-averse publishers and booksellers from handling it at all.

“There are no victims in manga  we should be free to write what we want,” said Yasumasa Shimizu, vice president at Japan’s largest publishing company, Kodansha, which is participating in the boycott. “Creativity in Japanese manga thrives on an ‘anything goes’ mentality.”

Manga taps into a history of erotica that dates at least as far back as the ukiyo-e prints of 17th- to 19th-century Japan, including Hokusai’s famous portrayal of a fisherwoman and octopi in a salacious encounter. But it was as recently as the 1980s that comic magazines like Lemon People introduced a wider audience to sexual manga featuring young girls.

“There is a culture, an industry that worships youth and innocence,” said Mariko Katsuki, who published a book last year chronicling adults who are attracted to small children. “Much of the attraction is nonsexual, but sometimes it becomes a dangerous obsession.”

The new Tokyo law, which applies to anyone under 18, bans the sale of comics and other works  including novels, DVDs and video games  that depict sexual or violent acts that would violate Japan’s national penal code, as well as sex involving anyone under age 18. The ordinance also requires guardians to prevent children younger than 13 from posing for magazines or videos that depict them in sexually suggestive ways.

Legal experts say that Japan’s laws against child pornography are lax by international standards. Japan has banned the production or distribution of any sexually explicit, nude images of minors since 1999, when Parliament passed a law in response to international criticism of the wide availability of such works in the country. But even now, unlike the United States and most European countries, Japan does not ban the possession of child pornography.