Hisahito, the nephew of Emperor Naruhito, is second in line to Japan's 1500-year-old Chrysanthemum Throne and the youngest of 16 members of the rapidly shrinking and aging imperial family.
The child who loved animals and bugs, especially dragonflies, is now a sophomore majoring in biology at the University of Tsukuba near Tokyo. He has been often spotted on campus with friends, sometimes carrying a bug-catching net or on his bicycle.
While he mostly concentrates on his studies, Hisahito started taking on some official duties.
He attended a palace banquet for Philippine President Ferdinand Marcos Jr in May, prayed for the atomic bombing victims in Hiroshima and joined a teenagers' camp in the southwestern Japanese city in August.
Hisahito is often compared to his hugely popular cousin, 24-year-old Princess Aiko, who has impressed everyone with her ability to interact with people and make them smile. She is the emperor's daughter and most Japanese want her to be his successor, even though as a woman she is ineligible.
The revised succession law enacted by Japan's Parliament in July lifts a ban on the adoption of male offspring from extremely distant former royal families. It lets female royals keep their status after marrying a commoner, so they can continue to undertake official duties, but their future partners and offspring won't be royals.
The revisions to the 19th-century law have been criticised as anachronistic and sexist and led to protests from Japanese who see the changes, which were backed by conservative Prime Minister Sanae Takaichi, as an attempt to eliminate Aiko from ruling while justifying discrimination against women and a patriarchal system.
Experts say the measures will put Hisahito and his eventual wife under enormous pressure to bear a male child as they determine the future of the imperial family.
