I'm trying to come up with a thesis topic but I'm stuck. I'd like to write my thesis about Japan and its national security. Or maybe its military. I'm just not sure what event I can focus on. I'd would really appreciate some ideas or events I can read up on.

This is a particularly propitious time to be studying Japanese security interests. With the rise of China as a global power and that country's assertions of sovereignty over the entirety of the South China Sea and over disputed island chains in the East China Sea (the latter a point of contention between China and Japan), Japanese officials are currently reconsidering their post-World War II commitment to pacifism. In addition, Japan is geographically very close to the Korean peninsula and the notoriously belligerent regime ruling North Korea. North Korea, as much of the world knows, is determined to continue to develop and build ever more sophisticated nuclear weaponry and the ballistic missiles needed to deliver those weapons to targets across the Pacific. In so doing, North Korea has been testing its nuclear-capable missiles over Japanese territory. In other words, Japan resides in a very dangerous neighborhood. Its commitment to pacifism, therefore, was certain to weaken.
Japan's constitution was largely imposed on the defeated remnants of the nation by the victorious and occupying United States. That constitution was written in such a way as to prevent the emergence of another militarily aggressive autocratic regime such as ran Japan before and during World War II. It worked. So disillusioned and defeated were the Japanese people by the end of the war that the United States could successfully pacify its former enemy. There were periods during the Cold War when Soviet activities prompted some in Japan to rethink its pacifistic policies. Those sentiments, however, were restrained. Today, as mentioned, Chinese and North Korean activities in disputed areas as well as the latter's aforementioned missile and nuclear weapons tests have pushed the Japanese into a corner, a situation exacerbated by the contraction in the size of the U.S. Navy, which maintains facilities in Japan and which has been instrumental in protecting Japan from its powerful neighbors.
A thesis on Japanese national security policy can easily draw on the wealth of available material on Chinese and North Korean military activities threatening to Japan. A logical thesis statement could be along the lines of, "geopolitical transformations over the past decade have forced Japan to reconsider its 70-year commitment to limiting its military capabilities to minimal self-defense requirements. Japan can be expected to debate changes to its constitution that would enable it to greatly increase its military capabilities--a development that would alarm those nations in North and Southeast Asia that remember all-too-well the horrors of Japanese militarism during the first half of the 20th century.
 
https://intpolicydigest.org/2016/08/01/senkaku-islands-dispute/

https://www.nytimes.com/2017/08/29/world/asia/korea-missile-japan-pacifism.html