The Japanese era system, which has been in use for more than 1,300 years, is increasingly considered to be unnecessary and no longer relevant to modern society by some as the Gregorian calendar has become more prevalent in the postwar period.

Some argue the "gengo" system, which initially symbolized what was considered to be the emperor's control over the period of time, is inconvenient compared with the Gregorian calendar, while others say it contradicts the postwar Constitution that stipulates sovereign power resides with the people.

(A staff member of calendar maker Todan Co. inserts the new era name "Reiwa" in a 2019 calendar)

In modern Japan, an era name stands for the length of an emperor's reign and is used widely in official documents. The current Heisei era, which means "achieving peace," commenced on Jan. 8, 1989, and will end on April 30, when Emperor Akihito abdicates.

The government announced Monday the next era will be named "Reiwa" when it starts upon Crown Prince Naruhito's ascension to the throne on May 1.

Japan names new imperial era beginning May 1 "Reiwa"

Q&A: What is gengo and why is its change so important in Japan?

Chronology of major events related to changes in modern era names

It was unveiled in advance to ensure there is a necessary preparation period for government offices and companies to update their calendar systems and to avoid possible confusion among the public.

The Japanese era system was first introduced in 645 but lost its legal basis when the country was defeated in World War II and occupied by the U.S.-led Allied forces from 1945. Although it was kept as a custom, arguments against the system grew.

In 1950, a Diet panel had full-fledged discussions for the first time on whether to keep or do away with the gengo system.

Most testifiers such as the president of the Science Council of Japan, a senior official of the Foreign Ministry and university professors were in favor of doing away with the system.

They argued that using the Gregorian calendar would be more convenient from an international perspective. But eventually, discussions at the parliament did not result in the system being abolished.

In 1979, the debate was rekindled when the Cabinet of the then Prime Minister Takeo Fukuda moved to legislate the gengo system.

Kamejiro Senaga, a vice chairman of the Japanese Communist Party at that time, opposed the move at a parliament session, saying it "goes against the Constitution and reverts to a prewar era of monarchism centered on the emperor." But the anti-era system movement did not gain momentum and the system was legalized later that year.

Forty years after the system became legal, there are still strong opponents to gengo.

"(Japanese society) is no longer controlled by an emperor," said Hiroshi Kozen, a Chinese literature professor emeritus of Kyoto University and a member of the Japan Academy, an organization that recognizes eminent researchers.

"The era system should reflect people's desire and we have to start from discussing why we need it," the 82-year-old said.

Koichi Shin, a 60-year-old member of a group opposed to the imperial system, called for the abolishment of the era system, saying it violates the Constitution.

Takafumi Horie, 46, a Japanese entrepreneur once touted as a maverick business leader, said in a magazine article that Japan should adopt the Gregorian calendar in official documents because using gengo is inconvenient.

Last Wednesday, three people -- a lawyer from the central Japan prefecture of Nagano, a journalist from Tokyo and a company executive -- filed a lawsuit with the Tokyo District Court to seek suspension of the era name change.

In the suit, the plaintiffs claimed changing the era name in every imperial succession "destroys a sense of time held by each individual" and violates Article 13 of the Constitution that guarantees all of the people shall be respected as individuals.

"The people are living in a time of world history," said Jiro Yamane, the lawyer among the plaintiffs. "The Japanese era system is unnecessary."

Asked which they prefer to use in their daily life, 39.8 percent of respondents in a Kyodo News opinion poll conducted in January said they want to use both gengo and the Gregorian calendar, while 24.3 percent opted for the former and 34.6 percent the latter.