The fastest-selling Game Boy (about $29.99) title in Nintendo's 10-year history, "Pokemon," is stomping through America like Godzilla with a migraine.

What started two-and-a-half years ago in Japan as a Nintendo video game for the pocket-size, hand-held Game Boy system is now a $4 billion industry there. A game built around finding, capturing, collecting and trading "Pocket Monsters," -- as known in Japan -- "Pokemon" is no longer kid's stuff.

In Japan, "Pokemon" characters have cavorted through comic books, feature films and on the sides of Japan Airlines planes. The "Pokemon" cartoon series made international news last December when a flashing special-effects sequence induced convulsions and nausea in more than 700 viewers.

"Pokemon" hit local stores about a month ago. At Toys R Us, store director Thomas Luiz said, "It's very popular with kids 15 and under; it's hard to keep it in stock."

He said the kids are bringing in their parents and taking them directly to the Pokemon aisle. "It looks like kids are buying them for themselves," he said. So if they're meant to be Christmas gifts, Luiz said, "I don't think they're going to have much of a surprise."

The only item more popular this season, is the Furby, the furry interactive plush doll.

"I can never pick these things ahead of time," Luiz said. "The craze drives the sales."

"We expect to sell between a million and a million-and-a-half by the time we get to Christmas," says George Harrison, vice president of marketing for Nintendo of America Inc., based in Redmond, Wash.

What's behind this riot of retail activity? "Pokemon" combines video-game technology with the role-playing, trading and collecting elements.

Here's how it works: Two versions, one red, one blue, are available. To win, players must have access to both versions. Players try to become the World's Greatest Pokemon Trainer by searching for, raising and battling with 150 different hidden monsters. To win, a player must collect all 150 monsters, which can take weeks or months.