I'd be interested to know if you found an answer to this.
Some more information here but aimed more at Japanese
http://sjlife.exblog.jp/15553702/
Under the current Japanese rules if you have less than 25 years of contributions in the Japanese pension I think you don't receive anything. My understanding is you can count the years in the Swiss system and if both combined are more than 25years than Japan will pay the fraction of the pension. In the case of non-Japanese I'm not sure if you have to be residen in Japan to actually receive the payments.