Naishi no tsukasa (内侍司)
Naishi no tsukasa was one of the cutcherry in government-regulated organizations in Japan. It was one of the 12 offices belonging to kokyu, empress's residence fixed by Ryo code (administrative laws) and consisted of only court ladies.
Court ladies in Naishi no tsukasa served the emperor closely and dealt with affairs like introducing messages, transmitting imperial orders and managing imperial formal events. This position was a kind of emperor's secretary and talented ladies who were well versed in academics and etiquette were appointed.
The divine mirror, which was modeled after Yata no Kagami (the eight-span mirror; one of the Imperial regalia) as one of the three sacred imperial treasures, was kept in Unmeiden (Naishidokoro), therefore, court ladies in Naishi no tsukasa had to protect and keep the mirror.
Thus, this divine mirror was called 'Naishidokoro.'
The rank of court ladies in Naishi no tsukasa was not so high according to the rule of Ryo. But little by little, their official duties became important and the rank became much higher during the reign of Emperor Heizei in 807. That was one of the causes of the Kusuko Incident.
After the mid Heian period, structure of the 12 offices belonging to kokyu was reorganized and the Naishi no tsukasa became only one practical official in kokyu. Naishi no kami/shoji, a chief of Naishi no tsukasa was treated almost as an empress, and Naishi no suke who was a deputy chief had the characteristics of an emperor's concubine.
Chief of Naishi no tsukasa
The official rank of Naishi no kami was Jugoi (Junior Fifth Rank), then upgraded to Jusanmi (Junior Third Rank). The prescribed number was two. Mostly daughters of Sekkan-ke (the families which produced regents) were selected. Originally, only Naishi no kami could deal with the official duties such as introducing messages and transmitting imperial orders, and Naishi no suke and other lower ranked court ladies could not deal with them.
Later, as Naishi no kami was treated almost as an empress, Naishi no suke and the lower ranked court ladies dealt with the actual duties. Between the late Heian and Kamakura periods, Naishi no kami was not appointed.
Naishi no suke/Tenji
The official rank of Naishi no suke was Jurokui (Junior Sixth Rank), then upgraded to Jushii (Junior Fourth Rank). The prescribed number was four. Mostly daughters of court nobles such as dainagon (chief councilor of state) and chunagon (vice-councilor of state) were selected.
The third ranked officials
Official rank of Naishi no jo was Jushichii (Junior Seventh Rank), then upgraded to Jugoi (Junior Fifth Rank). The prescribed number was six, consisting of four regular officials and two irregular officials. Normally, 'Naishi' means Naishi no jo.
Naishi no jo for joro (high rank female servant in the Imperial Court) with the First Rank was called 'Koto no naishi' or 'Nagahashi no tsubone.'
They always served for emperors and were in charge of Naishi no kami's roles such as introducing messages and transmitting imperial orders, and transmitted the official orders to Kurodo (Chamberlain). After Naishi no kami and Naishi no suke became a mere facade, actual roles of Naishi no tsukasa were pursued centering on Koto no naishi. Koto no naishi had more power than daitenji, who was a high rank woman servent in the Imperial Court, externally during the Edo period.