Facebook and Mr. Zuckerberg are about to get a blast of publicity in Japan, although perhaps not of the most positive sort. “The Social Network,” the movie that presents a less-than-flattering portrayal of Mr. Zuckerberg, opens in Japan this week.

Facebook has stepped up efforts to tailor its service to Japan. A Japanese version of the site, translated free by volunteers, was introduced a few years ago, but the company opened a Tokyo office in February to customize the site for Japan. (Facebook’s Japanese site, for example, allows users to display their blood types, considered an important personality trait here.)

Some users complain that Facebook’s Japanese-language site is awkward to use.

People like Maiko Ueda, 26, a Mixi devotee, see little reason to switch. Ms. Ueda, who works at a stationer based in Osaka, logs into Mixi at least once a day to read other users’ “diaries,” which resemble status updates on Facebook, albeit in longer form. She uploads pictures of her American shorthair cat, and sometimes writes about her day in her own posts.

But most people on Mixi do not know her real name, nor have they seen what she looks like. In her five years on Mixi, she has never uploaded a photo of herself.

She has heard of Facebook but says she is suspicious of “how open it seems.”

“I don’t want to give it my real name,” Ms. Ueda said. “What if strangers find out who you are? Or someone from your company?” She spoke on the condition that her Mixi user name would not be revealed.

In a survey of 2,130 Japanese mobile Web users by the Tokyo-based MMD Laboratory, 89 percent of respondents said they were reluctant to disclose their real names on the Web. Specialists say that while Facebook users in the United States tend to recreate real-life social relationships online, many Japanese use Web anonymity to express themselves, free from the pressures to fit into a conformist workplace.