If the pope can retire, why can't Japan’s ageing emperor?

Pope Benedict XVI did it. Dutch Queen Beatrix did it. So why is it so hard for Japan’s elderly emperor to abdicate?
Public broadcaster NHK reported last month that Emperor Akihito, 82, wanted to abdicate “in a few years”, something unprecedented in modern Japan.
Ordinary Japanese sympathise with his apparent desire to hand over to Crown Prince Naruhito but the idea faces stiff opposition from Prime Minister Shinzo Abe’s conservative base.
Conservatives have already raised objections to changing the law to let Akihito step down, citing problems ranging from his title and possible strife with a new emperor, to worry the next step would be letting women succeed and pass on the throne, anathema to traditionalists.
Even more, conservatives fear that a debate over the imperial family’s future would divert political energy from Abe’s push to revise the postwar, pacifist constitution, which they see as a symbol of defeat, but admirers consider the guarantor of Japan’s democracy.