Taiso means imperial funeral of an emperor, empress, grand empress dowager, empress dowager and empress consort.
Modern court ritual and related acts describe it as 'taiso (imperial mourning).'
It was an ancient tradition to build a hinkyu (temporary imperial mortuary) to enshrine the remains of the deceased for one year. After the cremation was introduced when Emperor Jito passed away, the procedure was simplified and the ordinary enshrinement period became 30 days. The procedure was changed to conform to Buddhism at the funeral of Emperor Shomu. Since the Heian period, a taiso had been held at a temple that he or she had built before he or she had passed away. Sennyu-ji Temple in Kyoto became a venue for a taiso after the time of Emperor Gokogon of the Northern Court (Japan). Doso no sei (imperial command of burial) was restored while maintaining the cremation style after Emperor Gokomyo of the Edo Period. The ceremony style was also changed in line with the burial style in the time of Emperor Komei. Until then, the funeral rites had conformed to Buddhism. As a result of the Meiji Restoration and the relocation of the capital to Tokyo, however, Sannen-sai Festival (a ceremony held three years after an emperor's death) for this emperor was held at the Imperial Court, which had been transferred to Tokyo by that time, according to Shinto rules. Based on the Shinto ceremonies for Empress Dowager Eisho and Emperor Meiji, the Imperial ordinance of mourning was enacted in 1909, and then the Imperial ordinance of funeral rites was established in 1924. The ordinances stipulated that the term 'hogyo' (demise) referred to the death of an emperor, a grand empress dowager, an empress dowager, and an empress consort, and the term 'taiso' referred to their funerals. Both the Imperial ordinance of mourning and the Imperial ordinance of funeral rites were abolished due to the revision of the Imperial Household Law after the war. However, rites based on these ordinances were adopted as customary practices. When Emperor Showa passed away in 1989, the national ceremony called Taiso no Rei (the Rites of an Imperial Funeral) was held separately from the Imperial Family's ceremonies called Sojoden no Gi and Renso no Gi in order to comply with the principle of the separation of politics and religion according to the Constitution of Japan. In fact, the ceremonies were held sequentially.