There's an active Japanese custom bike culture that has a style all its own. Starting with some of the same bikes we would start with over here in the U.S. and many that get no attention here whatsoever, they put their own unique mark on these machines. A bit of cafe racer with lots of street tracker mixed in, too.
These images illustrate some of the work and they all come from a Japanese site called Bratstyle. There's a Honda CB750, a Triumph 650, a Yamaha XS650 and SR600. Quite a few Kawasaki W650s get the treatment, too. The entire site is in Japanese so I can't tell you very much except the bikes they do are excellent. They don't appear to be big money machines but there's a lot of work involved. It looks like they sell parts and accessories and judging from their gallery, they turn out quite a few bikes.
It's an interesting style, check out their site and see what you think.
More photos and link below: