Japanese protesting for peace are opposed to militarization of their country. Not since World War Two has Japan militarized for war or sent its soldiers overseas to fight in other people's wars. The Liberal Democrats under Prime Minister Shinzo Abe and his Defence Ministry and Foreign Affairs Department have just passed a national security bill allowing Japan to fight overseas. This has divided the country between the Liberal Democrats in government and the Peace movement, who are opposed to the changes. Abe says the bill should get approval to prevent China on the rise throughout South East Asia from expanding into Japanese territory.
You have to look back at the history of Japan to understand why this is happening in the 21st century, decades after it surrendered to the Allies. Japan's pacifist constitution was written by America when it was an occupied country, following the Pacific war. Ultra-nationalism began to rise in the mid-30s, with the Imperial expansion into Asia that led to the second Sino-Japanese war and continued to the Pacific war. America did not want a repeat of this.
Since then, Japan’s spending on the military has only been one per cent of its GDP. However, with the recent passing of the security bill, it has just had a boost of sixty billion dollars. Japan keeps an independent foreign policy, whether the international community agrees with it or not.
The Antinuclear movement aligned itself with the Peace group opposed to changing the Constitution for self-defence. However, Abe had the majority needed to pass Article 9 of the new security bill. The opposition to the bill don’t want the Japanese people to be drawn into another conflict.
references
http://www.nytimes.com/aponline/2015/09/16/world/asia/ap-as-japan-security-bills-.html?_r=1
http://www.review.upeace.org/index.cfm?opcion=0&ejemplar=24&entrada=126
https://en.wikipedia.org/wiki/List_of_countries_by_military_expenditures