When I was a boy, rail-fans were not that common. It was said that trainspotting was a weird hobby. Rail-fans including trainspotters seemed to be weirdos, but these days, the situation has totally changed. According to sociological research, there are 2 million rail-fans in Japan. It's 1.6 percent of the total population. They are no longer weirdos, just ordinary people.
What's a current weird hobby in Japan? To name a few of them would be easy, but to decide the best, that would be difficult. If I were to pick, it's manhole covers observing. There are various kinds of manhole covers throughout Japan. Some of them are historically important; others are beautiful. I'm not a manhole covers lover, but I'm at least fond of colorful manhole covers with local designs. Please look at the photo as an example. I recently found it in Kawasaki City, Kanagawa Prefecture. It was installed by the local waterworks bureau. The design was taken from one of the historic "ukiyoe" works painted by Utagawa Hiroshige (1797-1858). It's very beautiful.
On the way to Kawasaki, I came across the EMU 1000 series (1st batch) at Hacchonawate station on the Keikyu line. It had a beautiful red colored aluminum body with a white stripe on the center of its side. I prefer this red colored aluminum body to the bare stainless bodies, which were adopted from the 6th batch of the 1000 series.
The artistic manhole covers and beautiful trains... they are symbols of Kawasaki City.
An artistic manhole cover in Kawasaki City