Yahoo maps for jpn
You can get 4G SIM cards at airports or at the giant electronics stores like Yodobashi and Bic Camera. Many of them are designed for tourists and should have English telling you what you get, though I don't remember. They should be cheaper than using data roaming.
If you're eligible for Telstra Air, it's a good idea to activate it before you travel, there's a decent amount of free Fon hotspots you can connect to:
https://fon.com/maps/
If you're going to Tokyo, you can also pick up a free pocket Wi-Fi device for three days at a time for ¥5000 deposit (you have to bring your passport as well) from various places within Sumida Ward:
http://visit-sumida.jp/wp-content/uploads/2015/06/wifi.pdf
Thanks for the help, guys ✨
Currently at the airport eating a really good toastie and staring at the aeroplanes out the big windows, it's actually calming me down a bit. Hoping for a safe and smooth flight.