The most popular option seems to be
Softbank where you rent a SIM card for
105 yen per day and then pay
105 yen per minute. Free incoming calls. You need to return the SIM though which is inconvenient. They do have data plans but you have to use the 703SHf phone which they rent out for
250 yen per day. The data then costs 0.32 yen per packet - have no idea what that means ^^; The phone has a PC browser so that you can check your GMail or whatever. Unlikely that you can tether the phone to your laptop though.