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 (親任官).
The investiture ceremony is held in the Matsu-no-Ma room (松の間) of the Tokyo Imperial Palace. Several officials are present to witness the entire ceremony.
The ceremony first starts with the candidate 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 candidate acknowledges the Emperor by bowing and then turning to their side to receive their letter of appointment from the former Prime Minister (or the current Prime Minister in the case of the appointment of the Chief Justice) containing the Emperor's Privy Seal and signature. The candidate 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 (usually the Deputy Prime Minister) will take over the role as the former Prime Minister in the investiture ceremony.
A similar ceremony called the Imperial Attestation (認証官任命式 Ninshōkan-ninmei-shiki) 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 ceremony is required to be attested by the Emperor under the Constitution.