On Aug. 27, 1914, the Japanese navy set up a blockade of Tsingtao, a German-run port on the coast of China, after declaring war on the German state just four days earlier. The Japanese navy then waited for the British navy to arrive at Tsingtao, and the two combined forces attacked and then captured the German-held port. The Japanese went on to seize most of Germany's overseas colonies in the Pacific and began setting up its own empire, which of course put the country on a collision course with the United States and the United Kingdom.
The German-Japanese rivalry is an odd one to think about, given that the two states were allies in World War II, but it was so short-lived that the term “rivalry” is probably the wrong term to use to describe their fight in World War I. Even today, Germany and Japan are sometimes thought of as rivals in the global economy because both countries specialize in high quality goods, and they oscillate between having the third or fourth largest economy in the world (nominal GDP) behind the United States and China, but rumors of a commercial beef between Germany and Japan today are non-existent.