Biglobe Mobile are a Japanese cellular provider running on the NTT DoCoMo network. They offer a range of long-term SIM plans, as well as a prepaid data SIM called the “Ninja SIM” for tourists.
The Biglobe Ninja SIM comes in 3GB and 7GB packages, with the data valid for 30 days. You can top up if you run out. Voice calling is not possible with this SIM, nor is SMS messaging. The Ninja SIM can be purchased at retailers across Japan, and is easy to set up—just pop it into your phone, set the APN (easy instructions are provided with the SIM), head to the given webpage to activate the service, and you’re good to go.
Biglobe’s long-term SIM plans offer the choice of data-only or data+voice contracts, with a minimum period of 12 months. Data packages range from 3-30GB/month. SMS messaging can be added on as an extra service to data-only SIMs, and comes built into data+voice plans.
Note: The level of English-language support available for long-term plans from Biglobe Mobile is unclear. Intermediate or advanced Japanese-language ability is recommended.