This question gets asked quite a lot, and while there is always more that can be said, you may enjoy these previous answers:

Why wasn't Emperor Hirohito tried for war crimes following WWII, and what reasons did General MacArthur have for steering things this way? as answered by /u/TheWinStore

Just Finished Herbert Bix's Hirohito and the Making of Modern Japan. What's the Scholarly Consensus? Is Hirohito a War Criminal? as answered by /u/kieslowskifan

After the Empire of Japan's defeat in WW2, why wasn't Emperor Hirohito put on trial for war crimes? as answered by a deleted user

Why was Emperor Hirohito allowed to keep the throne after Japan's unconditional surrender in World War 2? as answered by /u/restricteddata

Hirohito often gets lumped in with Hitler as an evil dictator in popular parlance, but to what degree can we actually lay the blame for Japanese atrocities like Nanking and Bataan on him? as answered by /u/Catfulu