KEY POINTS:
Japanese Emperor Akihito commemorated the 20th anniversary of his reign overnight, but with no notable plans other than a trip to his father's grave.
The anniversary comes as Akihito, 75, has cut back his official duties because of an irregular pulse and bleeding from his stomach - symptoms imperial doctors have attributed to "mental stress".
He has also undergone surgery and treatment for cancer.
Akihito ascended the Chrysanthemum Throne after his father, Hirohito, died in 1989.
