Nit. He’s the head of government, not the head of state.
In Japan, the Emperor is the head of state.
The Emperor is only a figurehead - much Like the Queen of England. They lack any power over their nations.
Absolutely. However, the Queen and Emperor are both heads of state and outrank their Prime Ministers, who are only heads of government.
The US is unusual in that the President fills both roles, although this is true in some other countries also. In most republics there is a president with little direct political power who nevertheless outranks his premier in a formal sense. Israel, India, Ireland, Iran, Iraq are some examples just from the I’s.