Upwards of half a million Japanese share Takahashi’s unlikely passion. The runaway popularity of PostPet 2001, Sony Communications Network’s hypercute e-mail program, has been a stunning phenomenon, even in a land with Japan’s insatiable sweet tooth for virtual pets like Tamagotchi, Pokemon and Aibo the robot dog. Since the debut of PostPet’s first version in late 1997, the program has sold some 580,000 copies in separately packaged form. An additional million or so copies have been sold in “bundled” form, preinstalled on the hard drives of new computers. Aside from Windows and a few other software essentials, PostPet is Japan’s best-selling program ever. “None of us expected such a success,” says Michio Kitamura, the keeper of PostPet’s menagerie.

Each store package of PostPilot holds a pair of CD-ROMs–one to give a friend, since interactivity is more than half the fun. When you install it, you choose an animated pet (teddy bear, bunny, kitty, tortoise, robot, hamster, penguin or doggie) to inhabit a customizable onscreen room. When your friend sends mail to you, her kitty-cat (say) prances into your puppy-dog’s room bearing a message and a token of pixillated affection such as a flower or a tiny bug. After Fido accepts the delivery, the two pets do a little dance together before Fluffy exits. When you send a reply, Fido vanishes from his room temporarily. When the message reaches your friend’s computer, you get confirmation of delivery: an onscreen note from Fido saying he has been out playing with Fluffy.

Almost no stores outside Japan carry the ¥3,980 program. But you can download an English version from a Sony-affiliated Web site (www.sony.com.sg/postpet/). Chinese and German versions are also scheduled for release before January. Like any other household animal, PostPet has a few shortcomings. It’s slow and lacks the versatility of more serious mailers. It won’t let you set up multiple mailboxes to sort incoming and outgoing messages, and your pet can’t take mail to more than one address at a time. But such flaws don’t faze the happy owner of Blue the tortoise. “My pet more than makes up for a little inconvenience,” says Takahashi, who uses a standard, no-nonsense e-mail program for real business. Blue is his companion, not his workhorse.