The robe in the phot is the Emperor's "o-hiki-nohshi".
Since the "suso (=skirt)" of the "o-nohshi" robe was pulled, it was named "o-hiki(=pull)-nohshi."
In case the Imperial messenger is sent to the Imperial mausoleums of Emperor Jingu, Emperor Jinmu, and four generations of the former Emperors at the time of the ceremony of accession to the throne, the Emperor wears it.
The ensemble of the ceremonial costume: see chart-2 on page 436.