More revered than the Emperor. More powerful than the Yen. More popular than Pokémon. Say... Hello Kitty

For more than a century, in journals, books and seminars, political scientists have debated the question: who holds real power in Japan? The conventional answer is that it is exercised by the people via their elected representatives - but that is plainly naïve nonsense. Some look to the Emperor, still a figure of quiet reverence. Others point to big business, or to the bureaucrats who work the levers of the mighty economic machine.

For more than a century, in journals, books and seminars, political scientists have debated the question: who holds real power in Japan? The conventional answer is that it is exercised by the people via their elected representatives - but that is plainly naïve nonsense. Some look to the Emperor, still a figure of quiet reverence. Others point to big business, or to the bureaucrats who work the levers of the mighty economic machine.

But they are all wrong. I know, for I have seen the face of true power in Japan. It is white and pink, with little black whiskers and no visible mouth. It is the face of Hello Kitty.

Many people outside Japan, particularly those with young daughters, will be familiar with Kitty, a small cartoon cat whose only distinguishing feature is a flower behind her left ear. In Britain, she can be found on stationery, school lunch boxes and sweetie tins. Hello Kitty is the kind of character favoured by little girls of five and six, before they grow up and move on to Barbie. To look at, there is nothing strikingly Japanese about her. But Japanese she is and, in her own country, she is an icon, an empress and a multi-million pound business.

The Pokémon characters, Super Mario, the Tamagotchi digital egg - these are crazes that bloom, flourish for a year or two, and then fade away. The first remarkable thing about Hello Kitty is her staying power: since her birth in 1974, her image has appeared on 26,000 different products, with 500 new ones appearing every month. The second secret of Kitty's success is her constituency. For in Japan, this most childish of characters - a few soft lines and a blob of colour - is a cult item not among little girls, but grown adults.

The ubiquitous Hello Kitty mobile phone is only the tip of a giant pink iceberg of grown-up Kitty merchandise that encompasses every aspect of consumer existence. There are Kitty pianos and Kitty cupboards, Kitty toasters and Kitty hotplates, Kitty curry and Vin Kitty, a rather indifferent-looking French plonk with a pink label. There are Kitty watches, Kitty cufflinks and silk Kitty ties decorated with tasteful blue lozenges and tiny, almost invisible Kitty images. You can buy Kitty calculators, Kitty lap-top computers, Kitty dictaphones, Kitty executive luggage and - my favourite - the Hello Kitty electric document shredder.

Recently, Kitty delirium has begun to appear in other parts of Asia: in Singapore last year there was a riot when a branch of McDonald's ran out of give-away Hello Kitty promotional figurines. Who is this awesome creature and what is the secret of her immense appeal? In search of some answers, I travelled to the grand shrine of the Kitty cult - the Hello Kitty theme park, 40 minutes from central Tokyo, called Sanrio Puroland.

Almost two million people come every year to Puroland, which dominates the uncharismatic suburb of Tama. On one side of the road is a grey office owned by a telecommunications company; opposite are the pink turrets of Kitty's castle. You pay your 4,400 yen (£30) and walk into the entrance hall where energetic young people in giant Hello Kitty suits cavort for the visitors. I am in luck, for downstairs the daily performance of the Hello Kitty Dream Revue, a 20-minute opera featuring the eponymous heroine, is about to begin.

The story gives some idea of the Hello Kitty ideology and the values that give her such a grip on the national imagination. The action opens in a magic forest where Hello Kitty, her boyfriend (inexplicably called Daniel) and a supporting cast of furry copyright characters are looking for fairies. But everything goes terribly wrong when one of Kitty's friends (an indeterminate orange being which may or may not be a gerbil) pulls up a mushroom and unleashes a troop of evil goblins. Kitty's soothing words, however, convince the goblins of the error of their ways, and the plot winds up with the heroine flying around on wires attached to the ceiling and everyone else singing a song about how, if you are nice, your wishes will come true.

All this went down well enough with the several hundred children in the audience, but what worried me were the adults. For there they were, watching the show and queuing to have their photographs taken in the Kitty costume studio - young couples, in their twenties and thirties, laden with bags from the Puroland shops, and unaccompanied by children.

I talked to Noriko and Takahiro, maths teachers at a Tokyo school, both 26 and here on their second visit to Puroland. Ask anyone why they like Hello Kitty and the answer you always hear is that she is "kawaii" - cute, the quality most admired in young Japanese women. "Adults like her because she is nostalgic," said Noriko. "It reminds us of when we were children." "She's so simple and uncomplicated," said Takahiro. "She can appeal to anyone."

Noriko was born in the same year as Kitty, but it was not until she was a teenager that she started collecting, and not until even later that she could afford her favourite Kitty items - the TV, the phone, the pink Kitty lingerie.

Indeed, it was in the early Nineties that Hello Kitty hit the big time with adults, the very same time that Japan's recession kicked in, and the post-war economic bubble was pricked once and for all. Is it a coincidence that Japan's worst years have been Kitty's best? Is that her secret - that, in times of hardship, she represents precisely nothing: no mouth, no personality, no edge, a blank pink canvas of pure cuteness, a substitute for taste, imagination, and even thought itself?