This was all I could find on them, its one of those abscure companies that made guitars in the 60's Japan era.
A little more info has surfaced. Back in the 1960s, there was one factory in Japan that basically made almost all Japanese guitars, ukes, banjos, etc. Yamaha and Ibanez and even some Martin guitars were all made there. Many of the models were the same for different companies, just different finished and brand name changes. Quality was generally very good for their products. Apparently that's where Diastone had its instruments made as well.
According to Wikipedia:
In 1957 Hoshino Gakki manufactured what would be considered the first of the modern era Ibanez guitars. In 1962, Junpei Hoshino, Yoshitaro's son, opened the Tama Seisakusho factory to manufacture electric guitars and amplifiers. The Tama Seisakusho factory produced a line of guitars that included clones of several popular guitars, including the Martin Dreadnought. At the time they were also manufacturing Star Drums, available in either the Imperial or Royal models. Hoshino Gakki stopped making guitars at the Tama Seisakusho factory in 1966 (but continued making Drums) and from then on contracted outside guitar factories, like there main factory and exclusive one in Japan, FujiGen , to make guitars.
FujiGen started in 1960 with the production of violins and classical guitars. In 1962 FujiGen started production of electric guitars. In the 1970s FujiGen started making guitars (OEM) for companies such as Hoshino Gakki (Ibanez), Kanda Shokai (Greco guitars) and Yamaha. In 1977/1978 FujiGen went into a joint venture with Roland Roland Corporation to produce guitar synthesizers. In 1981 FujiGen opted out of acoustic guitar production to mainly concentrate on solid body guitar production. In 1981/1982 FujiGen obtained the Fender Japan contract which lasted until 1996/1997. In mid/late 1992 FujiGen obtained a part of the Orville by Gibson contract which ended in 1998 and from then on have made Epiphone Japan solid body guitars, some Gretsch models and their own branded FgN guitars. FujiGen still do OEM guitar manufacturing for companies like Ibanez and Epiphone but in much smaller quantities than in the past. FujiGen has 3 factories in the Matsumoto area, the Omachi factory, the Hirooka factory (established around 1992) and the main FujiGen factory. FujiGen has also manufactured Variax guitars for Line 6.
My son wanted to learn guitar so my mom bought this from someone you had an add for it. SHe thinks she paid $250. How much do you think it is worth. My son could never learn on it as 12 string and he is left handed and could not get a grip on it.