Goshogo is a title given to an Imperial family in Japan.
Goshogo is a title given to a member of the Imperial family in Japan when he or she is young, and presently it is given to Emperor's children and Crown Prince's children but not to children of Miyake (families allowed to have the status of Imperial family). Basically it is the combination of one kanji (Chinese character) and the character '宮/Miya' (Imperial prince/princes). For the source of the kanji, scholars make selection from classical books such as Gokyo (the Five Classics texts of Confucianism) and submit several proposals to Emperor from which he chooses one to give it to a recipient.
The Goshogo (and the name) of Imperial Princess Aiko, the oldest daughter of Imperial Prince Naruhito who is the present Crown Prince, is said to have been chosen by the Emperor by taking into consideration of the wish of the Crown Prince and Princess.
It is unknown when this custom was started, but it seems that it had already been fixed in the Edo period.
The titles of Emperors in the modern times.