I own a Fuji GS645, a folding RF with 75mm f3.5 lens and a Fuji GA645, a motorized AF model with a retracting 60mm f4 lens.
The GS645 has excellent optics, but I found it incredibly fragile. It broke twice on me in very moderate conditions and it's now shelved as I'm not willing right now to throw more money at it. It gave me a few good pictures, but I've found it unreliable and expensive to repair.
The GA645, while very plastic with noisy motors, has been excellent to me. The lens is very sharp and, unlike the GS, takes filters without hard-to-find unique adapters. I post here one of my favorite human shots with my GA:
Afraid I'm no help with local shops in Tokyo, but I'm sure somebody else can pitch in.