helping
Hi, I was just searching for the same ringtone and found it on a website called crostel.com it's free. you just have to join and enter your number when registering. search for "one missed call" and click on the samples until you find the Japanese version and then click on the small phone icon and it will send it to your phone in the form of a text with sound and you can save it to ringtones or sounds, which ever you choose.
Just take away the spaces, I'm not able to put url's in my posts yet.
I think it's the second one on top on the second page once you've searched 'one missed call'. I hope that you'll be able to use it.