Prince Hisahito turns 20 as Japan's government reinforces male-only succession rules

Prince Hisahito celebrated his 20th birthday on Sunday as Japan's government solidified its male-only succession rules. The nephew of Emperor Naruhito is second in line to the country's 1,500-year-old Chrysanthemum Throne and the youngest of 16 members of the shrinking imperial family.

Aloof and studious, Hisahito is a sophomore majoring in biology at the University of Tsukuba near Tokyo. The animal-loving teen has been frequently seen on campus with friends, sometimes carrying a bug-catching net or cycling. While focusing on his studies, Hisahito has begun taking on official duties, such as attending a palace banquet for Philippine President Ferdinand Marcos Jr. in May and praying for Hiroshima bombing victims in August.

Comparatively, Hisahito is often seen alongside his popular cousin, Princess Aiko, 24, who has won admiration for her ability to connect with people. However, Aiko, the emperor's daughter, is ineligible to succeed to the throne due to her gender, despite Japanese public preference. The recent revision to the Imperial House Law, passed by Parliament in July, has been met with criticism as anachronistic and sexist.

The changes permit female royals to retain their status if they marry a commoner and continue undertaking official duties, but their partners and children will not become royalty. The new rules, supported by conservative Prime Minister Sanae Takaichi, have been seen as an attempt to exclude Aiko from the line of succession while justifying discrimination against women and a patriarchal system.

Hisahito's future, along with his eventual wife, will likely face significant pressure to have a male child as they determine the imperial family's future.