For international trade, TTPP is the most commonly-used B2B directory site in Japan
TTPP (Trade Tie-up Promotion Program) is an international business matching website operated by Japan External Trade Organization (JETRO), and allows people both in Japan and abroad to search through over 30,000 business proposals, with a free of charge.
Once you register for membership, TTPP allows you to view contact info as well as business proposals (Sell or Buy) of other members. You can send inquiries to the contact persons, and it is also possible to post your business proposals. The registration and use of the database are available for free.
For your information, the words “proposals for buy/sell” are “Anken 案件” in Japanese, and the word “Inquires” is “Hikiai 引き合い” in Japanese. These words often used in daily business life in Japan.
TTPP International Business Matching Site by JETRO
A List of B2B portal sites in Japan - by JETRO