Who was president of Japan in World War 2?

Hirohito was the Emperor.
There was no president in Japan; Japan was an empire, and the Emperor Hirohito was on the throne. Until the end of the war, Hirohito was considered to be literally divine; a god. He publicly renounced his divinity after the war, on radio. See the link below and to the left. Today Japan is a parliamentary democracy. Emperor Akihito is Head of State, and Prime Minister Shinzo Abe is Head of Government.