Crown Princess Masako, who is still recuperating from a stress-induced illness, is set to fully attend an imperial garden party on Friday for the first time in 15 years, the Imperial Household Agency said.

The 54-year old wife of Crown Prince Naruhito has left the event early in recent years. But as long as she feels well, the crown princess will make a full appearance at the biannual party, which will be the last hosted by Emperor Akihito and Empress Michiko before an imperial succession next year.

The emperor and empress are expected to exchange greetings and converse with guests for about an hour during the party, held at Akasaka Imperial Gardens in Tokyo, once each in spring and autumn.

The crown princess, a commoner and former career-track diplomat, began receiving treatment in December 2003. In 2015, she attended an autumn garden party for the first time in 12 years but since then has only interacted with guests for several minutes at garden parties.

In recent years, however, she has engaged in more official duties and shown signs of a solid recovery.

According to a senior agency official, the crown princess skipped a two-day trip through Thursday with the crown prince to Yamagata Prefecture to maintain her condition.

The crown prince, the emperor's eldest son, will ascend the throne on May 1, and the crown princess will become an empress, after the emperor abdicates the previous day based on his desire to do so due to his advanced age and failing health.

As the emperor will be busy with ritual events before his abdication, a garden party will not be held in the spring next year.

In this year's event, the emperor and empress are inviting about 2,100 guests including astronaut Norishige Kanai and playwright Koki Mitani.