I have a friend that is in Japan right now and he sent me this picture. It looks heavy…
In 1991 or so, a Japanese kid rode across the United States on something like that. His father had built him a big wheel to fit his small size. Still might have been cheaper than buying a Schlumpf… 
I don’t remember much details of his trip, and am not sure if that’s the cycle, but it could be. I think it was '91 because he was passing near Iowa around the same time as the USA convention there. Or it could have been '96 then, the other year it was there…
Not one belonging to Takayuki Koike by any chance?
it looks fun!
No, he wouldn’t have needed the chains; he’s tall enough. I think the unicycle he used for the 100 mile record might have belonged to IUF founder Jack Halpern (or might be the one he has now). It looks basically like an old Coker but with older-style main cap bearing holders, and one of those flattish rims that kind of sticks out on the sides. Very heavy! And his cranks were probably less than 125mm (and probably cottered).