Besides oil and gas, the Japanese are also obsessed with the fishing rights associated with these islands.
Most of the recent spats with China have involved Chinese fishing vessels encroaching on the fishing zones associated with these islands that are controlled by the Japanese. Here is a video of a Chinese fishing boat ramming a Japanese Coast Guard vessel near one of these disputed islands (Islands controlled by Japan that China is disputing.):
YouTube - Truth of the Senkaku incident 5 - Second Ram
Japan has a huge population and few natural resources. This means that they have to import a large percentage of their food. Consequently, they have huge insecurities regarding retaining control over what few resources that they do have.
Immediately post WWII, the Japanese suffered horribly due to lack of enough food to feed their population and people did starve.
Here is a scene from the Japanese Animated movie, "Grave of the FireFlies," where a young boy is doing his best to keep his sister from dying of starvation.
YouTube - Grave of the Fireflies