She reaches into the bag and removes one of her pets. It resembles a flattened blue egg with a tiny grey screen and three buttons. Blinking from the display is a small round blob with a smiley face. Beside it, cunningly pixillated in liquid crystal, is a steaming virtual turd.
Michiyo Takana, who works in the office next to mine is 21, slim and fashionably dressed. But more desirable than her beauty, wardrobe, or youth-- to a few million of her contemporaries, at least - are the two bleeping lumps of plastic she carries around with her.
Since its launch at the end of last year, the Tamagotchi electronic pet (the name translates as something like "Eggsy") has become the most sought- after, and the most fought-over, object of Japanese desire. The first production run of 750,000 models, originally priced at yen 1,980 (pounds 10.50), has long since been exhausted. Factories in Hong Kong and Singapore are working frenziedly to produce 4 million more by next month. The manufacturer, Bandai, plans to sell 13 million over the next year.
Black market Tamagotchi are changing hands at unbelievable prices. Ms Takana has been offered pounds 250 for her blue-and-pink model, and word is that the most popular white Tamagotchi is changing hands for almost pounds 800.
Unquenched demand is creating a new breed of Tamagotchi criminal. While promenading recently in Shibuya, Tokyo's greatest teenage hangout, a girl in school uniform attempted to snatch the toy from around Ms Takana's neck.
Last week a helicopter, several patrol cars, and a dozen police officers were involved in the pursuit of a gang of bandits who had made of with one of the virtual pets. The four delinquents turned out to be 14 years old.
The toy (full name: "Hyper Interactive Digital Pet Tamagotchi") has already spawned two how-to advice books on its rearing and nurture.
Each game begins with the appearance on screen of the Bebitchi ("Babesy"), the most primitive stage of the creature; the aim is to keep it alive for as long as possible, watching it grow through various stages of life right to maturity as an Oyajitchi ("Grampsy").
The growing animal has various needs, of which defecation is only one. Intermittent beeps indicate that the pet needs to be fed, disciplined, or entertained. These are accomplished by means of the buttons and a series of symbols; when the Tamagotchi is ill (perhaps from being left for too long with a full nappyload) you treat him by moving a cursor and clicking on a tiny syringe.
The uniqueness of the game is the length of time over which it is played. The game beeps for attention a couple of times an hour, but it can be muted or put into hibernation when more pressing matters are at hand, and it sleeps for 12 hours a night. One day is the equivalent of one Tamagotchi year, and so the best brought up eggsies are now several months old, but they are frail and unpredictable creatures. Overfeeding can create a spoiled or delinquent eggsy, which will demand ever more attention; neglect, as with all pets, can be lethal. "The last time, it died when I was singing karaoke," says Miss Takana.
"I couldn't hear it beep, and we came out, paid the bill, and it was dead." [There can be no mistake when this sad moment arrives - a small digital gravestone appears on the electronic screen.]
"I was so shocked that I cried. I was genuinely upset and I decided that the next time it dies, it will be because of fate, or sickness, not because of my neglect."