As the twee cafes and boutiques in this quiet corner of Tokyo's Marunouchi business district fill with groups of "office ladies", it is easy to see how out of place Yuki Sakurai would look in the company of the blue-suited salarymen grabbing a quick noodle lunch beneath the nearby railway tracks.

For one thing, the 28-year-old business consultant is impeccably turned out, from his perfectly knotted striped tie to his scuff-free brown leather shoes, bought after a champagne breakfast with some female friends.

He is patience personified when passers-by do a double take while he poses for the Observer's photographer. When I ask him when he decided to become an unrepentant "grass eater", he doesn't flinch. It is not an unkind reference to his diet. Sakurai is a proud member of a new tribe of Japanese men who have eschewed traditional notions of masculinity and adopted a gentler, more "feminine" persona.

He is a soshokukei danshi – herbivorous boy – a term coined two years ago by the commentator Maki Fukasawa to describe the proliferation of men who, in appearance and attitude, bear little resemblance to the two dominant Japanese male groups of the past century: soldiers and their peacetime offspring, corporate warriors.

The typical herbivore cares, sometimes a little too much, about his appearance, eats sparingly, prefers afternoon tea with female friends to an evening spent drinking and shows little interest in the obsession that consumes so many of his peers: sex.

Sometimes referred to as ojo-men (ladylike men), they are mounting a counter-attack against the baby-boomer generation, whose lives revolved around company, colleagues and, a distant third, their wives and children.

Some dismiss the genre as the product of inventive marketing for male cosmetics, skin-tight fashions and, at the most militant end of the spectrum, male bras, minus the lacy frills.

But Megumi Ushikubo, author of The Herbivorous Ladylike Men Are Changing Japan, says men such as Sakurai are the vanguard in a quiet social revolution. Ushikubo, president of a market research firm, reckons that as many as 60% of Japanese men aged between 20 and 34 display at least some herbivorous tendencies.

"They don't have the material aspirations of previous generations," says Ushikubo, whose interest in the phenomenon was piqued by calls from companies unable to sell fast cars or alcohol to young men. "They have no appetite for food or sex. You ask them what they want out of life and they say, 'Nothing much'."

Rather than bond over beer, the average herbivore invests his time and money in activities once regarded as the preserve of young women: shopping trips, dining out, personal grooming and cultural pursuits.

The herbivores have no personal experience of the bubble years of the 1980s. Instead, Sakurai's generation reached adulthood as the economic edifice started to crumble, and unemployment and contract work replaced jobs for life and twice-yearly bonuses.

"Young men went through a crisis of confidence towards the end of the 1990s," Ushikubo says. "The economy isn't performing well, so they don't see the point of working too hard, because they think things will never improve."

Less amenable to sociological analysis is the herbivores' ability to suppress their carnal instincts. Sakurai, who says he has been single for several years, puts it down to an overdeveloped fear of rejection and commitment.

"I have lots of female friends I'm attracted to," he says. "But you weigh up the risks and benefits and come to the conclusion that things are best left as they are. I'm lucky to work in an industry where there's no stigma attached to being single and no pressure to get involved with someone."

The rise of the herbivorous man has met with mixed reactions. Traditionalist employers complain that they lack the work ethic of older generations, while commentators blame their sexual abstinence and relative thrift for the low birthrate and the weak economy.

Some women, too, say they prefer their men rougher around the edges. A popular revival in interest in Japanese history has made unlikely pin-ups of feudal warlords from the distant past.

Sakurai doesn't take the criticisms seriously. "It's too bad about the birthrate, but that's also a sign that the women are enjoying more freedom than before. It's as if social stigmas attached to both sexes have been lifted."

The herbivores' appearance in the Japanese social firmament is not without its benefits. "They really care about their families," says Ushikubo. "They don't believe that the state will be able to do its bit for their parents or themselves after they retire."

As he approaches his 30s, Sakurai reluctantly accepts that his grass-eating days may be nearing an end. "My younger brother just got married, and I can't see myself being single in my 40s," he says. "But I'm in my comfort zone right now. Why would I want to change that?"