Crown Prince Naruhito and Crown Princess Masako attended the coronation of Tonga's new king on Saturday.
The coronation service for King Tupou VI was held at the Free Wesleyan Centenary Church in the capital, Nuku'alofa.
The Japanese couple attended a luncheon hosted at the royal palace later in the day and chatted with Crown Prince Tupouto'a Ulukalala and other members of the Tongan royal family.
Crown Princess Masako, who has been receiving treatment for a stress-induced illness for more than a decade, is on her first overseas trip since 2013.
The Crown Princess will skip other events involving her husband in consideration of her condition, according to the Imperial Household Agency.
She last traveled overseas to attend the coronation of Netherlands King Willem-Alexander, her first official trip in 11 years.
In a positive sign, however, the Crown Princess' participation in official duties has recently been on the rise.
The Crown Prince and Princess are scheduled to return to Japan on Monday.