Her marriage to Kei Komuro on Tuesday will mean she becomes a commoner in keeping with laws saying female members of the imperial family cannot keep their royal status after marriage.
Princess Mako and Komuro met while attending the International Christian University in Tokyo in 2012.
Before his introduction as the royal fiance, Komuro was better known as the “Prince of the Sea,” after appearing in a beach tourism campaign for the city of Fujisawa, south of the capital Tokyo.
Photographs of Princess Mako taking a walk on the imperial grounds with her younger sister were released by the Imperial Household Agency, but no comment was given by the princess to mark her birthday.
The three-year engagement of Princess Mako and Komuro was marked with scandal and controversy, which started when a tabloid reported that Komuro was embroiled in a money scandal.
The Imperial Household Agency said in a news conference held in early October that Princess Mako had developed post-traumatic stress disorder from the intense media scrutiny her engagement came under.
The couple is expected to move to New York, where Komuro works as a lawyer, after the wedding.