As Naruhito takes the throne, the imperial lineage has come under spotlight again. The Japanese throne is only passed down to male heirs, but the new emperor has just one daughter. Terrence Terashima reports from Tokyo.

Naruhito and Princess Masako received a Western education. Both studied at Oxford. Many Japanese expect him to be as devoted to the people as his father Akihito was.

But his succession to the throne has rekindled the debate on the imperial lineage. Japan will not have a crown prince.

Naruhito's younger brother, Fumihito will be first in line to the Imperial throne but he is not the son of the new emperor.

Second in line will be Fumihito's son, a 12 year old Prince Hisahito, who will not be a crown prince unless his father ascends to the throne.

With the fast aging imperial household, Hisahito will be the only young heir to the throne with the male lineage. Which means, unless he has a son, the world's longest monarchy might come to an end.

AKINORI TAKAMORI IMPERIAL HOUSEHOLD EXPERT "We have spent the last decade with only a single prince. The situation is very serious as it is likely he will be the only heir to the throne. It will put extreme pressure on him and his potential wife to continue the lineage. The government promised an early debate on the possibility of changing imperial household law and allowing a female emperor, but the ruling party wants to postpone until next year something that should have started already."

TERRENCE TERASHIMA TOKYO "A recent survey suggested that 70 percent of the public would support a female emperor or an emperor of female lineage both of which are currently prohibited by law. Government sources say they will consider starting the debate in spring 2020."

In creating Meiji Imperial House Law, such arguments were made that a female Emperor's dignity would be diminished by the presence of a consort, for Japanese popular sentiment and social norms gave precedence to the male.

Activists now argue that it is time for Japan to end subjection of women, especially when it threatens the existence of the monarchy.

The government has made a pledge that the debate will start at the earliest convenience. But with the mounting political agenda, it is looking to be still some time away. Terrence Terashima, CGTN Tokyo.