The predominantly male crowd, perusing shelf upon shelf of gadgets, fetish DVDs and costumes, would have been even more nervous had they noticed that a few of the booths aimed to increase sexual pleasure for -- not with -- women.
Japan has a major sex toy industry, estimated to be worth some four trillion yen (34 billion dollars) a year, but female customers are a neglected market.
Not so at last weekend's three-day Adult Treasure Expo 2007, where women visitors had their pick of brightly coloured vibrators, accessories and other sex aids.
"Compared with 11 years ago, the situation for girls has improved greatly," says Minori Kitahara, 36, a feminist activist who is trying to change things in her own small way.
She runs LovePieceClub, a sex toy shop for women in Tokyo.
Unlike the other exhibitors here, Kitahara's display is not in-your-face. Her vibrators are mostly pastel colours of pink, light blue, or white and are round and smooth.
She was also selling vibrating tiny plastic ducks, both yellow and pink -- offering women a bit of naughty fun for the bathtub.
The most aggressive item she was offering was probably handcuffs -- but decorated with soft fur.
While men are far more frequent buyers of sex toys in Japan, Kitahara says that women have also become increasingly open about fulfilling their sexual desires since the time she opened her shop in 1996.
"I specifically select items that are free from harmful chemical substances and do not make loud noises," she explains.
Kitahara's booth was hardly the norm at "Sexpo", where nearly 160 companies exhibited products and services otherwise traded underground, most of them all about -- not for -- women.
One stand offered a line-up of dummy women with child-like faces and disproportionately huge breasts, wearing only tiny pieces of fabric or leather. Another offered videos with girls tied up and screaming.
"They're for people with fetishes," Takako Yoshikawa, a spokeswoman for Baby Entertainment, explains without a hint of discomfort. She adds that many companies in the industry have female spokespersons in hopes of a softer image.
Koji Uchida, an advisor at the Plum company, said he was selling DVDs featuring sex with "amateur" girls, not professional pornographic actresses.
"Of course the target is men," Uchida said. "People like to watch these amateur girls because they show their virginal naivete."
Sex toy vendors in Japan are hoping to take their cue from the United States, where the growth of the female market has been a major driver of the multibillion-dollar sex toy industry.
In the 1970s, women hosted Tupperware parties in suburban America. Today, they invite girlfriends over for "passion parties", where plastic vibrators and lubricants -- not ice-cube trays and soup containers -- are on offer.
Takako Kimura, a manager of software provider Hotesseshop, said women's demands for sexual items had increased over the years here.
She said many of her female customers had even resorted to buying gay porn due to the dearth of material geared towards heterosexual women.
"Many videos made for men show sex that is too animal-like. Women like to fantasise about good-looking men, about something unrealistic," she said.
Kitahara acknowledges that the industry is still "all for men", but is pleased that the options open to women have vastly improved.
"It wasn't so long ago that a girl had to summon all her courage to buy a vibrator. Now she can choose an item that's friendly to the female body," she says.