J-Net21, the business information site of the government agency for small and medium enterprises, describes how continuing trade is often set up in Japan. The parties put the rules common to all their dealings in a kihon keiyakusho, a basic contract. Each single deal then runs on an exchange of order forms and acknowledgments, or on a simple contract.
The site adds that each deal made under the basic contract still forms a contract of its own. These are called kobetsu keiyaku, individual contracts.