Hoeki no ho (robe with a round collar, stitched sides and a ran, worn by an emperor and high-ranking (縫腋袍)
Hoeki no ho is one of the Japanese robes of chofuku (clothes worn by the people who come to work at the court on a regular basis), and a ho (round-necked robe worn by members of nobility and the Imperial Court), which has sewn sleeve seams, an outer robe and fabrics called ran (brocade) running sideways around the hem.
The origin of the Japanese 'chofuku' is "Shanfu" (everyday court dress) in Tang ('chofuku' in Tang was a different thing of the same name), and the robe of this Shanfu derived from Kohuku (traditional clothes for Kojin [who lived in Northern China in ancient times]) (according to "Meng Xi Bi Tan" (Dream Stream Essays)). The robe of Kohuku originally had open sides, but since Yuwen Hu, an member of the Imperial Family in Northern Zhou, proposed to the government, this hoeki no ho was made (according to "Zuisho" (the Book of the Sui Dynasty), etc.).
In drawings of the Tang period, one can see that many guarding officers and kangan (eunuchs) wore these robes with ketteki (1. unstitched, open-sided traditional Japanese clothing, or clothing with such an open side; or 2. a robe worn by military officials with a round collar, unstitched open sides and no ran) and civil officers used hoeki no ho with ran, but it wasn't necessarily appropriate to suggest so.
In Japan, it is considered that 'kinu' in the chofuku for an imperial prince, members of the Imperial Family in the 'Garment Code' of the Yoro ritsuryo code (a code promulgated in the Yoro period) was hoeki no ho, and 'ao' in chofuku for military officers was ketteki no ho (an outer robe for military officers) and worn by military officers or children before genpuku (the coming-of-age celebration).
In the early Heian period, those of Ikai (court rank) or higher rank could wear hoeki no ho except for while on guard and those in Sanmi (Third Rank) or higher could wear hoeki no ho even while on guard.
The name 'hoeki' isn't popular in China, but in Japan this name was already found in "Wamyo-sho," a dictionary compiled during the Heian period.