The long-term survival of the world's oldest monarchy will depend on a schoolboy when Japan's current emperor abdicates next week, reviving calls for an end to laws that bar women from the throne.

Twelve-year-old Hisahito, son of Crown Prince Akishino, will become second-in-line to the Chrysanthemum Throne when Akishino's elder brother, Naruhito, inherits the crown from their father on May 1.

Akishino will be first in line but is already 53.

"The whole future of the Imperial family depends on one little boy -- that he will remain healthy and be willing to marry and have children with his wife," says Ben-Ami Shillony, a professor of Japanese at the Hebrew University in Jerusalem.

Japan's Prince Hisahito with his parents, Prince Akishino and Princess Kiko, before attending the entrance ceremony at Ochanomizu University junior high school in Tokyo on April 8, 2019.

Conservative and patriarchal Japan excludes women -- who make up 13 of the 18 members of the royal family -- from taking the throne. But this wasn't always the case.

Empresses ruled Japan at various times over several centuries until they were barred in 1889.