The Empire of the Sun is a 
Japanese event.
It triggers when Japan reaches Great Power status. The only possible choice Banzai! gives 5 prestige and make all POPs lose 3 Militancy. It is good to mitigate the militancy created by the Meiji Restoration, and Japan will often become a great power straight after westernizing.
The event describtion states: Japan, Empire of the Rising Sun. For many years, since the black ships of Gaijin first appeared on our shores, our nation has been sailing in the wake of powers greater than and beyond our own. With our recent ascention to Great Power Status the tides of fortune have turned. From now on let the winds repulse and break any foreign wave that dares wash over the sacred shores of the Great Power of Japan!