The gengo is used during the duration of the emperor's reign and even though Japan uses the Gregorian calendar like the rest of the world, the gengo is still widely used in calendars, newspapers, and official documents. This is where various multimedia franchises comes in as the eras of various franchises, such as Kamen Rider and Godzilla use the current gengo to divide the eras of their respective franchises. To put it simply, the next entry to any of these franchises is the first entry of the new era.
The current era, Heisei Era means "achieving peace", which started on January 8, 1989, the day after Emperor Showa, the father of the current emperor passed away. The era will end on April 30, 2019, the day Emperor Akihito will abdicate his throne.