Hikikomori.

"A person sequestered in his room for six months or longer with no social life beyond his home."

...Japanese culture and sex roles play a strong part in the hikikomori phenomenon. "Men start to feel the pressure in junior high school, and their success is largely defined in a couple of years," said James Roberson, a cultural anthropologist at Tokyo Jogakkan College and an editor of the book "Men and Masculinities in Contemporary Japan." "Hikikomori is a resistance to that pressure. Some of them are saying: 'To hell with it. I don't like it and I don't do well."' Also, this is a society where kids can drop out. In Japan, children commonly live with their parents into their 20's, and despite the economic downturn, plenty of parents can afford to support their children indefinitely - and do. As one hikikomori expert put it, "Japanese parents tell their children to fly while holding firmly to their ankles."...

Many hikikomori also describe miserable school years when they didn't, or couldn't, conform to the norm. They were bullied for being too fat or too shy or even for being better than everyone else at sports or music. As the Japanese saying goes, "The nail that sticks out gets hammered in."...

In other societies the response from many youths would be different. If they didn't fit into the mainstream, they might join a gang or become a Goth or be part of some other subculture. But in Japan, where uniformity is still prized and reputations and outward appearances are paramount, rebellion comes in muted forms, like hikikomori. Any urge a hikikomori might have to venture into the world to have a romantic relationship or sex, for instance, is overridden by his self-loathing and the need to shut his door so that his failures, real or perceived, will be cloaked from the world. "Japanese young people are considered the safest in the world because the crime rate is so low," Saito said. "But I think it's related to the emotional state of people. In every country, young people have adjustment disorders. In Western culture, people are homeless or drug addicts. In Japan, it's apathy problems like hikikomori."