Prepaid SIMs are not available from any of the major carriers. SIM rentals are available from Softbank for ¥105/day. Inbound calls are free and local outbound calls are ¥105/minute. Data is very expensive at ¥0.32 per 128 bytes, or roughly $25 per megabyte! Softbank will charge your credit card and provide a detailed invoice 2-3 weeks after completion of the rental. For more info on rentals through Softbank, see: http://www.softbank-rental.jp/en/.

The SIM rental works well for me as my primary need is to receive calls.