Mountain Accidents in Japan
There is currently no offical source that lists mountain accidents, distress calls, fatalities and missing hikers in English. I recoomend checking this website "oreyama" with google chrome translation if you're curious.
Please make sure you always have rescue insurance. The numbers below speak for themselves. I personally use "coco heli" which comes with a gps beacon too. The cost is reasonable with 5.500Y per year. If you use my code "58064" and sign up through their friendship introducation program you can save the enrollment fee of 3.300Y.