Japan’s Princess Aiko, often cheered like a pop star, turned 24 on Monday.

Her supporters want to change Japan's male-only succession rule, which prohibits Aiko, the emperor's only child, from becoming monarch.

Along with frustration that the discussion on succession rules has stalled, there's a sense of urgency. Japan's shrinking monarchy is on the brink of extinction. Naruhito’s teenage nephew is the only eligible heir from the younger generation.

Experts say the female ban should be lifted before the royal family dies out, but conservative lawmakers, including Prime Minister Sanae Takaichi, oppose the change.

Hideya Kawanishi, a professor at Nagoya University, told The Associated Press that "though it's not spelled out, what they're saying is clearly in favor of male superiority; that's their ideal society."

Aiko has gained admirers since debuting as an adult royal in 2021, when she impressed the public as intelligent, friendly, caring and funny.

Support for Aiko as a future monarch increased after her first solo official overseas trip to Laos in November.

Earlier this year, Aiko also accompanied her parents to Nagasaki and Okinawa. She has followed the example set by her father, who places great importance on passing down the tragedy of WWII to younger generations.

Setsuko Matsuo, a survivor of the Nagasaki atomic bomb, told The Associated Press she is "rooting" for Aiko.

"Her smile has saved me on so many occasions," she said.