Princess Nori is a "tenacious" lover of nature, while her fiance likes foreign cars and antique cameras, according to their friends.
Friends of the 35-year-old princess said she grew up under the strong influence of her late grandfather, Emperor Showa, and her father, Emperor Akihito, both marine-life researchers.
They said her love of animals appeared days before her second birthday. Her morning routine was to give bread crumbs to wild doves.
After entering elementary school, the princess kept a diary of observations of tadpoles captured in a pond on the premises of the Crown Prince's palace.
Later, she became enthusiastic about taking care of two dogs at the palace, the friends said.
"I want to become a guide-dog trainer," she wrote in a composition at Gakushuin Primary School.
The princess is still passionate about guide dogs. She has invited a trainer to the Imperial Palace in Tokyo to learn how to raise guide dogs.
Since 1990, she has bought annual tickets for charity concerts to support guide-dog training.
She studied ornithology in high school and devoted herself to bird-watching after entering Gakushuin University.
"She is tenacious," a friend said of her bird-watching.
The princess' fiance, Yoshiki Kuroda, a 39-year-old Tokyo Metropolitan Government official, is a close friend of her brother, Prince Akishino. They attended the same elementary school.
He is known to love foreign cars and antique cameras, parts of which he collects.
Kuroda never told any of his friends that he was engaged. They only found out when they read it in the newspapers or saw it on television.
In high school, Kuroda and the prince were both members of the photography and geography clubs.
After entering Gakushuin University, they established a nature and culture study club with research club members from high school.