It is not so easy to find a good application that will allow the use of offline GPS maps in Japan, especially since it can be hard to get access to any WiFi or telephone network when travelling and therefore make Google Maps inconvenient. From browsing the internet, I found the Maps with Me application that works on my Nexus 7 tablet. After installing the app (Maps with Me Pro) I zoomed over Japan as much as I could and it started downloading (Downloading Japan). After a while the map was completely saved so I explored a bit regions of Japan I am familiar with to see the level of detail. So far I am quite satisfied with the results. Once downloaded, those maps can be used without any internet connection.
I am looking forward to test the GPS features on the terrain since the Nexus 7 has a built-in GPS receiver but the Maps with Me Japan map should work with any Android or IOS device like the Iphone and Ipad with a built-in GPS receiver. I will write further about the features in the future as I get to now the app better.