Q: Context: Japan participated in World War I from 1914 to 1918 in an alliance with Entente Powers and played an important role in securing the sea lanes in the West Pacific and Indian Oceans against the Imperial German Navy as the member of the Allies. Politically, Japanese Empire seized the opportunity to expand its sphere of influence in China, and to gain recognition as a great power in postwar geopolitics.

Question: who's side was japan on in ww1?
Let's give stream of consciousness below
To answer this question, we should know that: Japan participated in World War I from 1914 to 1918 in an alliance with Entente Powers and played an important role in securing the sea lanes in the West Pacific and Indian Oceans against the Imperial German Navy as the member of the Allies. So the answer is Entente Powers.