soft bank office

i wish to know where soft bank office is located at futako tamagawa and how does someone check the expiry date and the amount of money left in soft bank (3g)prepaid

http://mb.softbank.jp/mb/shop/search/detail.html?shopId=0357177007

Futako tamagawa branch seems to be located right behind Takashimaya in Futako tamagawa. (The rectangle with lines shown at the right bottom of the map is the train station, the huge block in the middle is Takashimaya, and the red dot behind it is the Softbank shop.)

how does someone check the expiry date and the amount of money left in soft bank (3g)prepaid

When you arrive in Japan dial 1400 (tollfree) on the phone and follow the directions to check your balance and expiry. The menus can be set to English if they hadn't been yet, so just stay on the line if you initially hear Japanese.