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Oh, forgot to say - you can find detailed trail maps and hike times in this Japanese app:
https://play.google.com/store/apps/details?id=jp.mappleon.android.yamatokogen&hl=ja
Each map is 5 bucks but very good.
Once it's installed, press the top sign to choose the map. You should now have a list of maps (if not, there's a white button in the middle of a black bar at the bottom). What you want is map number 38 for Kamikochi.
Map 60 is Kirishima
Map 61 is Yakushima
** For Japan (only)**
山と高原地図 In app purchases. Sample map of Takao available for download. They print paper maps which I also bring with me. UI is all Japanese.
地図ロイド (chizroid) uses free GIS data from a local government server so needs a network. Haven't figured out how to pre-download all the map tiles I need. Custom maps usable! UI is "English".
In addition to what was already said here, a good hiking map phone app really helps with direction and progress.
Yamatokogen is a good one.
In case you are looking for digital maps, I bought some on the app "
山と高原地図" while I was living in Nagano.
It was amazing for hiking, showing the best trails for mountain climbing and realtime position along the trail.
This app has the trail map but it's mostly Japanese. Some location names may be labeled in English. You want map 52. It's 5 bucks per map.
https://play.google.com/store/apps/details?id=jp.mappleon.android.yamatokogen
I used the 山と高原地図 app when I climbed a couple mountains in Nagano. It worked great.
https://play.google.com/store/apps/details?id=jp.mappleon.android.yamatokogen&hl=ja&gl=US
Finding anything in English might be hard but here are few Japanese options:
Free maps here from Yamakei Online - give walking times, warnings, points of interest, toilets, parkings, etc. http://www.yamakei-online.com/yk_map/
Paid - Mapple Yamatokogen maps. Can be bought for half price and put on your android device or can be also bought in paper form. They also have walking times, and major mountain peaks are written in English. You can plot your trail with GPS on it. https://play.google.com/store/apps/details?id=jp.mappleon.android.yamatokogen&hl=en
Amazon sells physical copies for the full price but I'm not sure if the paper is waterpoof: http://www.amazon.co.jp/dp/4398762280