I am fortunate to have a very large park close to where my family and I live. A stroll past the pond and through the trees is the ideal way to work off a Sunday lunch. Part of the park is given over to a playground for youngsters, and I found myself there with my two young children last Sunday.
We were the only ones there at about 2pm, when a group of three middle-aged men and two girls in school uniforms arrived. They set down some aluminium cases and canvas bags beneath one of the trees. One man unpacked cameras, the second unfurled a reflector sheet and the third cast a critical eye over the photographic possibilities. The girls, meanwhile, had taken off their socks and were hitching their already short skirts even higher.
At just seven and three, my children are - thankfully - still innocent to the ways of the world and carried on flinging sand around. For anyone who has ever come face to face with Japan's pornography industry - which, frankly, is every adult, because the stuff is everywhere - it was clear that these people were not setting up a nature photo shoot.
Completely oblivious to our presence, the girls then went to 'work'. They slid down the slide - towards the photographer waiting at a low angle. They smiled coyly while showing their underwear at the top of the slide. They frolicked in the sand and stuck their tongues out suggestively atop the climbing frame.
The situation never went beyond suggestiveness - although I do have major problems about schoolgirls being sex objects. But my fascination was less to do with the photographer and his subjects, and more about the reaction of other people who by then had come into the park. Or rather, the lack of reaction.
Mothers with young children in tow never batted an eyelid. An old man walking his dog didn't do a double-take. A group of youngsters in their early teens were more interested in playing computer games. Families sat down to picnics on the grass. And no one said a word.
Japan is famous for being a society in which everyone is extremely conscious of the people around them - and not doing anything to upset the harmony of the wider group. But I fear the nation is taking that admirable concept too far. As an outsider, perhaps it is not appropriate for me to comment, but I found it remarkable that the photographer and his subjects were not shooed away.
Then again, perhaps I'm not the only one who feels this way. Producer Shinsuke Inoue was making a film in Yokohama city last month, starring actress Arisa Shimizu - a veteran of some 100 pornographic movies. In the middle of an ordinary afternoon, with the cameras rolling, Shimizu walked through parts of the city - stark naked. They, at least, were both arrested.