The Emperor, the Kotaishi (Crown Prince) and the Kotaison (the Emperor's grandson who is Imperial Heir) attain majority at eighteen full years of age. (Imperial House Law, Article 22)
Other Members of the Imperial Family attain majority at twenty full years of age (Civil Code, Article 4).
The style of address for the Emperor, the Empress, the Grand Empress Dowager, and the Empress Dowager is "His", "Her" or "Your" " Majesty."
The style of address for other Members of the Imperial Family is "His", "Her" or "Your" "Imperial Highness" or "Imperial Highnesses."
The Ceremony of Accession (Sokui-no-Rei) is held when the Throne is succeeded to. (Imperial House Law, Article 24)
View photos of the Ceremony of Accession here
The Rites of Imperial Funeral (Taiso-no-Rei) are held when the Emperor passed away. (Imperial House Law, Article 25)
Daitofu is the record of the lineage of the Emperor, Empress, and Empress Dowager.
Kouzokufu is the record of the lineage of other Members of the Imperial Family
The graves of the Emperor, the Empress, the Grand Empress Dowager, and the Empress Dowager are called "Ryo".
The graves of all other Imperial Family members are called "Bo".
Registers containing matters relating to Ryo and Bo are called the Ryo Register and the Bo Register.
For the crime of defamation or contempt of the Emperor, Empress, Grand Empress Dowager, Empress Dowager, or the Imperial Heir, the Prime Minister files a complaint in a court of law (Panel Code, Article 232).