Princess Aiko, the only child of Emperor Naruhito and Empress Masako, turned 18 on Sunday, enjoying her last year in high school as she prepares to move on for further studies at university starting next spring.

The cello-loving princess, currently a third-year student at Gakushuin Girls' Senior High School in Tokyo, vigorously carried out school assignments and studied for exams -- sometimes getting advice from the imperial couple, according to the Imperial Household Agency.

The princess rejoiced in her class victory at an athletics meet in September, while spectators were excited when she performed dance at a school festival in November, the agency said.

[Photo courtesy of Imperial Household Agency]

However, the agency's Board of Chamberlains declined to comment on which university the princess is considering attending.

During her trip to Tochigi Prefecture, eastern Japan, with her parents in August, the princess talked to a local female student of the same grade and they encouraged each other on their studies.

"We are in the same situation, so let us make our best," she was quoted by the agency as saying.

The princess saw a series of imperial rituals related to her father's enthronement on May 1, including the "Sokuirei Seiden no gi" ceremony for announcing the emperor's enthronement before international guests in October and a celebration parade last month, through media reports, the agency said.

[Photo courtesy of Imperial Household Agency]

Under Japan's Imperial House Law, the princess is not eligible to ascend the throne, which is restricted to males.

The shrinking number of heirs, down to three including her 13-year-old cousin Prince Hisahito, the son of Crown Prince Fumihito, is forcing politicians to discuss changes to the royal line of succession.

An October poll by Kyodo News showed that 81.9 percent of the public are in favor of Japan having a female emperor.

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IN PHOTOS: Daijosai rite by Japanese Emperor Naruhito