Let us assume that in an alternate World War One, Japan, being very opportunistic, joins the Central Powers. This gives Japan the opportunity to seize French Indochina, parts of the Russian far East, and perhaps even the Dutch East Indies.* The biggest Japanese difficulty to Japan in this scenario is Britain, which has a considerable large fleet. In order to allow Japan to join the Central Powers, we either need to get Britain out of the war entirely, or have Britian so tied up in Europe, that it cannot stop Japan. Take your pick. So, after the Central Powers win this alternate WW1, Japan now does have an Empire by 1918. How will this effect the development of Japan, and East Asia in general? Japan can now play up its role in fighting colonial Western powers, which could give the Japanese a lot of political credit with many Asians. Perhaps Japan could actually try and fulfill the role of "Protector of the Asian World" by creating the Greater East Asian Co-prosperity Sphere years earlier than OTL. I wonder, will Japan still want to invade China as IOTL? This will also cause conflict with the USA eventually, because the Philippines are smack in the middle of the new Empire. Butterflies galore!
So how plausible is this scenario, and what are the effects?
*The Germans intended to invade the Netherlands in the original Schlieffen plan, but it was changed IOTL.