During the Cold War between the Soviet Union and the United States, Japan's security policy was built in the framework of the Cold War. Japan concluded the U.S.-Japan security treaty in 1951 (amended in 1960) and became an ally of the United States. Therefore Japan became a member of the Western democratic Club. Japanese land itself is geographically the neighbor of the Soviet Union which was seeking a non-frozen sea in the South. The Japan Archipelago was then the breakwater. So, the Japanese security policy was primarily just to defend itself. The U.S. was satisfied with its Japan's role and did not ask more than that.
But in 1989, the same year of the passing away of Emperor Showa and the beginning of the Era of Heisei, the Berlin Wall which had divided the Western and the Eastern worlds fell down, and the end of the Cold War was proclaimed by President Bush and Chairman Gorbachev in Malta.
Then the global security situations changed dramatically. In 1990, Iraq invaded Kuwait, and the Iraq War occurred in 1991. The United States attacked Iraq with a coalition group and Japan participated only financially. After the Iraq War ended, the Japanese Self Defense Force was dispatched for the first time oversea for minesweeping. During the Era of Heisei, for 30 years, Japanese SDF participated in so many PKOs all over the world, for the first time in Cambodia in 1992, then in the Golan Heights, in the East Timor, and even in the South Sudan, etc. The Japanese government also dispatched the Maritime Self Defense Force for the anti-piracy operations and the Ground SDF to Iraq for its reconstruction after the War.
So, during the Era of Heisei, we can say that Japan's security policy expanded so much offshore, while China modernized and enlarged its military power and North Korea developed its missiles and nuclear weapons.
Then it come the Era of Reiwa, how are we foreseeing the Japan's security policy? Primarily, it should be focused on the stability and the peace of the Indo-Pacific region. The core is certainly the U.S-Japan alliance, but at the same time, Japan will deepen the relationship with other like-minded countries, such as Australia, France, England, India, Canada, etc. 'Reiwa' means a beautiful harmony, so Japan would have a harmonized security policy with these beautiful countries for the peace and prosperity in the Indo-Pacific region.