Until very recently, Japan did not offer *any* prepaid 'disposable' SIMs. They now allow prepaid non-rechargeable SIMs for foreign travellers which usually have a fixed 1-3Gb data usage, or a fixed airtime use. These SIMs also expire automatically after a fixed time period, usually 14 days or 30 days. The Japanese have long been highly paranoid about filthy foreigners using cellphones for *CRIME*.. literally even posting warning posters at train stations - "don't loan your phone to a foreigner" etc etc, when ironically it is obviously the yakuza who would be the worst offenders of 'burner phones'..

This has always meant a captive market for cellphone/SIM *rental* in Japan too. I have usually used JCR Corp based in Hawaii for my visits but there are several companies in the market. They will rent 3G/4G SIMs from DoCoMo or Softbank that work with any WCDMA2100-capable smartphone (many Nokias even supported this 10+ years ago).

Here's an example: B-Mobile Japan offering the prepaid fixed-use SIMs
http://www.bmobile.ne.jp/english/japan_sim.html


Basically, if you're a light data/phone user and visiting for 7 days or less, stick to the prepaid SIMs. If you'll be surfing, translating, mapping or visiting for 2 weeks or more, order a SIM from the rental agencies; it will cost a bit more but also be *unlimited* usage.