One festival that is most commonly spoken about among Japan, especially in anime is the Cherry Blossom(Sakura) Festival.
During this festival people have fun sitting under cherry blossoms, having barbecues and drinking and watching fireworks. .
Most of the time the cherry blossom festivals are held between March to May, though certain regions in Japan have them in January, February, and June, based on their location.
Festival dates are usually determined with reference to cherry blossom forecasts and vary from year to year.