I feel for you mate, the light pollution from a huge city like Tokyo must be absolutely staggering. It's amazing you can even see 20 stars from such a place.
I live in Adelaide, Australia, which is a city of a million people, but compared to a megalopolis like Tokyo it would be little more than an outback village. Yet I've looked up at the night sky from Victoria Square in the centre of the city and the light pollution there kills off all but the brightest stars too.
But Adelaide is also fairly compact; about half an hour's drive from the city and you're out in the Barossa Valley or the Mt Lofty Ranges, where the light pollution disappears, and the night sky from there is absolutely incredible. Here in the Southern Hemisphere we can't see the Plough or Polaris, but here the centre of the galaxy rides high overhead and the dust lanes of the Milky Way obscuring Sag A stand out in razor-sharp detail to the naked eye. You can clearly see the central bulge and the sky-spanning spiral arms stretching off to either side. And the Magellanic Clouds, our satellite galaxies, are also amazing to see - the Tarantula Nebula is an easy naked-eye object despite being 110,000 light years off.
Perhaps you can find a spot where you can see the night sky. I haven't been to Japan myself, but I have spent many an intriguing hour hopping around it on Google Earth, and I noticed there's a hiking trail to the top of Mt Fuji. You can even follow it on Street View since someone's gone up to the summit with a backpack pano camera.
Perhaps on your next time off you might take a little trip up to the summit there and see what the night sky looks like. At that altitude much of the atmosphere would be below you, which would not only make the stars clearer but would also eliminate much of the scattering that causes light pollution to be such a problem in your part of the world.
(Interestingly, I noticed that Mt Fuji is on the same longitude as Adelaide. My house is only 15 km west of the longitude line that runs through Mt Fuji, albeit thousands of kilometres south of it!)