Princess Aiko, 9, the daughter of Crown Prince Naruhito and Crown Princess Masako, was diagnosed with mycoplasmal pneumonia after being hospitalized for fever and coughing, the Imperial Household Agency said Friday.

When the princess will be discharged from the University of Tokyo Hospital has yet to be decided, although her fever has gone down and her symptoms are now stable, Kyoji Komachi, grand master of the crown prince's household, said.

Her mother is staying at the hospital with the princess, a fourth-grader at Gakushuin Primary School and the royal couple's only child.

Symptoms of mycoplasma pneumonia, caused by a pathogenic microbe, include intense coughing and high fever.

Prince's right of passage

The Imperial family held rite-of-passage ceremonies Thursday for Prince Hisahito, who turned 5 in September, at its shared house in Tokyo's Motoakasaka district.

Two ceremonies that were held, called "chakko no gi" and "fukasogi no gi," are Imperial versions of the traditional "shichi go san" rituals that celebrate kids' growth, at ages 7, 5 and 3.

Prince Hisahito is the son of Prince Akishino and Princess Kiko.

After wearing a white "hakama" skirt in the chakko no gi, Prince Hisahito, clad in traditional boys attire, took part in the fukasogi no gi, a ceremony for boys only, which was last held in 1970 for Prince Akishino.

The ceremonies had been slated for spring but were postponed due to the March 11 disaster.