i am going to japan this sunday. arriving haneda (airasia). is garmin useful?

I am in Japan now..hehehe..dream come true. yesterday at disneyland...too bad rain....now checking out sheraton grande. going to sheraton miyako. have to find Shirokanedai station. tomorrow will go mount fuji. already finish 20k yen...any help from people in japan would be appreciated. my fon on roaming and subscribing to NTT Docomo maxis 1 day data (RM38). i am on YM also (QAS800). information overload...hahaha...how to understand their train lines....