Watch out for the contract period "Shibari".
In Japan, there are three major Internet carriers, NTT, KDDI and SoftBank. They usually offer discounts if you agree to use their service for a certain period, for example, 2 years for the initial contract period etc,. This offer is of course a good deal but what you should be aware of is that they will charge a penalty fee for cancellation during the contract period. Also, the contract is automatically renewed and extended for another period before you know it. This contract style must be as the same as it in other countries.
For example, if you have a 2-year contract staring on August, the contract ends on August 2 years later when the contract period is automatically extended for another 2 years. If you don't want to renew the contract, you need to go through a cancellation procedure within the August. If you cancel the contract in September or later, you are considered to break the contract and will be charged for a penalty fee. If you want to cancel without paying the annoying fee, you will have to wait for August after the next year. We call this term commitment “Shibari” in Japanese.
Users can check the expiry by checking bills or his/her user account, but nobody pays much attention as long as an occasion comes up such as relocation.
Good News. They are reviewing their services
Since too many customers are unhappy about the automatic extension system, the major carriers and IPS providers are reviewing their service (as of June 2015). They are considering to send notification by e-mail to inform expiry, furthermore, users will be entitled to go through a cancellation procedure within two months instead of within one month, which means one month extended. Let's see how it will go.
High-Speed Network Carriers in Japan
*NTT West and NTT East provide different fiber-optic services each other, in operation covering in different areas. If you move from eastern Japan to western Japan, chances are that you will have to cancel the contract with NTT East, then have a new contract with NTT West. See their coverage - http://www.ntt.co.jp/product/category/area.html
Nuro by So-net
Mobile/Wireless Network Carriers in Japan
Related Info : Paid Wi-Fi Services
These services are usually provided without minimum contract period. The fee is paid on a monthly basis by credit card.
Yahoo BB Wireless LAN Spot Services
http://wireless.yahoo.co.jp/ (Japanese Website)
This service allows users to have Internet access at hot spots, including Japan MacDonald.
OCN Wireless LAN Spot Services
http://service.ocn.ne.jp/mobile/hotspot/ (Japanese Website)