Emperor Naruhito in the context of "Emperor"

A dynasty is a sequence of rulers from the same family, usually in the context of a monarchical system, but sometimes also appearing in republics. A "house" is a royal or noble family, not always ruling. Historians periodize the histories of many states and civilizations, such as Ireland (10th century), Roman Empire (27 BC – AD 1453), Imperial Iran (678 BC – AD 1979), Ancient Egypt (3100–30 BC), and Ancient and Imperial China (2070 BC – AD 1912), using a framework of successive dynasties. As such, the term "dynasty" may be used to delimit the era during which a family reigned.

Before the 18th century, most dynasties throughout the world were traditionally reckoned patrilineally, such as those that followed the Frankish Salic law. In polities where it was permitted, succession through a daughter usually established a new dynasty in her husband's family name. This has changed in all of Europe's remaining monarchies, where succession law and conventions have maintained dynastic names de jure through a female.

Masako (雅子; born Masako Owada (小和田雅子, Owada Masako); 9 December 1963) is the Empress of Japan as the wife of Emperor Naruhito.

Born in Minato, Tokyo, Masako was educated at Belmont High School in Massachusetts, United States, before attending Harvard College, earning a Bachelor of Arts degree with the distinction of magna cum laude in economics. She also studied law at the University of Tokyo and international relations at Balliol College, Oxford. After completing her studies, she worked for Japan's Ministry of Foreign Affairs as a diplomat.

Fumihito, Crown Prince Akishino (秋篠宮皇嗣文仁親王, Akishino-no-miya Kōshi Fumihito Shinnō; born 30 November 1965, Japanese: [ɸɯmiꜜçi̥to]) is the heir presumptive to the Japanese throne. He is the younger brother of Emperor Naruhito, and the younger son of Emperor Emeritus Akihito and Empress Emerita Michiko. Since his marriage in June 1990, he has had the title Prince Akishino (秋篠宮, Akishino-no-miya) and has headed the Akishino branch of the Imperial House of Japan.

Fumihito has a bachelor's degree in political science from Gakushuin University and a Doctor of Philosophy degree in ornithology from the Graduate University for Advanced Studies. In 1990, he married Kiko Kawashima, with whom he has three children: Mako, Kako, and Hisahito. In November 2020, Fumihito was officially declared the heir presumptive to the throne, during the Ceremony for Proclamation of Crown Prince (Rikkōshi-Senmei-no-gi) in Tokyo. Preceding his investiture as Crown Prince, the ongoing Japanese imperial succession debate had resulted in some politicians holding a favorable view on rescinding agnatic primogeniture, which was implemented in 1889 and reinforced on the constitution of Japan by the Allies after World War II. However, once Fumihito and Kiko had their son Hisahito in September 2006, he became next in the line of succession following his father. Fumihito's niece and Emperor Naruhito's only child, Princess Aiko, remains at present legally ineligible to inherit the throne, while debate about the possibility of having future empresses regnant continues.