Bring your own compatible unlocked wifi device and buy one or more bMobile sims. It's LOTS cheaper and they will deliver directly to the hotel or you can pick it up at the airport.

http://www.bmobile.ne.jp/english/index.html

If you use up your bandwidth or the SIM expires, you can buy a slightly different version over the counter at most all large electronics stores. In that case, ask the store clerk to activate it for you (the one ordered online doesn't require activation).