Does japan have a king or an emperor?
The current is Emperor Akihito.
A King is of lower rank than an Emperor. King Albert of the Belgians is of a lower rank than Emperor Akihito of Japan. An Emperor is a King of Kings, he/she has kings that are subordinate to them. It is a inherited title, usually pasted from father to son although there have been numerous exceptions to this such as Catherine the Great assending the thorne after her husband was killed.