I suppose we'd need to clarify/define terms/categories, and all that fun stuff. I'd start off with only frames actually built in Japan, kinda Duh!, but I know some Japanese dealers, with their own small brands, but they're building frames in Taiwan/China.
I guess it makes sense to include high-end bikes from non-Japanese brands, if built in Japan. WCC/Nishiki, WSI/Centurion, Specialized, Rivendell and maybe some others have spec'd some nice frames in Japan. Gets a bit complex since the Japanese source could change from model to model, season to season. You'd have to include some smaller brands like DIN/Echelon, importing two models made by Cherubim in the late '70s. In some ways it's a whole 'nother ball o' wax.
The big Japanese mfrs all made/make high-end frames, but they also made/offered full product lines, from entry-level & up. I think that's a category, but a small one:
Big Mfrs:
Araya (they sold high-end frames, not sure if they made in-house or subcontracted)
Bridgestone
Fuji
Miyata
Panasonic
Then you have mid-sized mfrs, maybe known more for their high-end product, but also made entry-level frames. Not sure how many fit here:
Katakura Silk (known for the all-chrome bikes brought home by many tall American GIs, but they had 10-12 builders and built inexpensive frames, too)
Anybody else?
Then maybe smaller shops, but with several builders, building mainly high-end frames, but also maybe doing some contract building for others?
Cherubim (3-4 builders, no longer doing much contract building, but built for Specialized and Fuji back in the day, and the DIN/Echelons)
Midori (hardly heard of, but I had some Japanese dealers who worked for Midori before they went under)
Miki (long out of business)
SanRensho (Konno had a few builders, I think, built the early Spec'l Allez and Sequoia)
Toyo (rarely see Toyo-branded frames, built for Specialized [40th Anniv Allez], Ritchey, Rivendell)
Tsunoda (I don't have a clear picture how big/small they were)
Likely more?
Then true one-/two-builder shops, and there are/were tons of these.
I buy the "Road Bike All Catalog 20xx" every couple of years, published by Ei Publishing in Tokyo. Lists just about every road/tri bike carried in Japan by every domestic/import maker. It includes a "Japanese Hand made Bicycle" section, with 21 builders for 2017. This should be a pretty complete list of viable builders currently building in Japan. I've heard of a bunch of them, don't know anything about some of them. I'm assuming that, like here in the US, there may be some younger builders in the market now. There is a Tokyo College of Cycle Design, opened in 2012, offering 2-/3-yr courses in bicycle design/production/sales. Cherubim/Konno teaches the framebuilding courses there, and they've been churning out potential framebuilders for 4yrs+ now. So there's probably a bunch of young'ns picking up torches now.
Builders in the 2017 All Catalog who I know, and/or who've been around for decades:
Akamatsu (Akamatsu-san was the hub specialist at Suntour, manged the WTB/Grease Guard hub disaster. Really nice guy, don't know if he's hand-building his own frames, or having someone else build them.)
Amanda (has been around for decades)
Cherubim (see above)
Ektar Proton (been around for decades)
Dobbat's (been around for a while)
Gan Well Pro (in Kyoto, had several builders and wider line in '85)
Level (been around)
Makino (was SanRensho/Konno's apprentice/builder, took over SanRensho after Konno died, eventually renamed business after himself)
Nakagawa (Osaka builder, often confused with Nagasawa)
Nagasawa (oddly, missing from the All Catalog 2017 list)
Ogre (young guys outside Kyoto, met them at NAHBS/Denver, showed a very weird grillwork frame)
Ravanello (been around)
Royal Norton (mainly touring/rando frames?)
Samson
Silk Cycles (don't think there's any connection with Katakura Silk?)
Vigore (Kansai/Osaka?)
Vivalo (Kansai/Osaka, I think)
Watanabe (from Kyushu, lovely frames)
In the All Catalog list, but I never heard of 'em:
Abukuma
Corner Bikes
Emme Akka
Equilibrium
Dontzer
Kualis Cycles
Macchi Cycles
Montson
Quark
Schmitt
Shin
Stratos
Sunrise Cycles
There's some names I know, don't know current status, and some that are long gone.
Everest
Midori (see above)
SanRensho (see above)
Between NAHBS, Japan visits and bikes in-house, I have craploads of related pix on flickr. I'm getting sleepy, so I'll just post a few here. Check through my albums for more. Be aware that a lot of my builds are resto-mods, so you're mainly checking out the frame details.
Cherubim Sportif/'16
Cherubim Steel Master/'12 Show Bike
Cherubim/Shinichi Konno:
Nagasawa-san in workshop, and drinking, 2016:
Nagasawa Special Keirin/'14:
Nakagawa Special Road/'94: Nakagawa-san's personal bike, on loan...
Echelon Odyssey (green) and Spectra (blue), by Cherubim/'80. The Spectra is mis-decaled as a Cherubim:
Level @ NAHBS/2014:
