Imperial Investiture
The Imperial Investiture is an official inauguration ceremony whereby the Emperor of Japan formally appoints the Prime Minister of Japan or the Chief Justice of Japan to office. In practice, the Prime Minister is nominated by the Diet, while the Chief Justice is nominated by the Cabinet. The Emperor is constitutionally required to appoint the nominated person, without the right to decline appointment.
During the time period of the Empire of Japan, as the Emperor was the source of executive authority, there were also investitures held for military officials. Such appointees were called the Shinninkan.
Ceremony
The investiture ceremony is held in the Matsu-no-Ma room of the Tokyo Imperial Palace. Several officials are present to witness the entire ceremony.The ceremony first starts with the Prime Minister nominee formally greeting the Emperor upon entering the room. The Emperor greets back upon their approach and addresses that he or she is about to be appointed to office. The Prime Minister nominee acknowledges the Emperor by bowing and then turning to their side to receive their letter of appointment from the outgoing Prime Minister containing the Emperor's Privy Seal and signature. The Prime Minister nominee turns back to face the Emperor, bowing and receding, before making their way to the entrance and then bowing again before leaving the room. The Emperor then leaves the room followed by the other officials.
For the appointment of the Prime Minister, both the Speaker of the House of Representatives and the President of the House of Councillors are present. If the current Prime Minister is re-appointed, then a Minister of State will take over the role as the former Prime Minister in the investiture ceremony.
A similar ceremony called the Imperial Attestation is held for the appointment of the Ministers of State, court judges and other officials. Although they are formally appointed by the Prime Minister, the Constitution stipulates that the ceremony must be attested by the Emperor.