Aosamurai were samurai warriors who served domestic governing institution of nobles and court nobles.
It is considered to be a synonym of 'Namazamurai', which appeared in "Okagami" (Great Mirror; a historical tale), and in diaries such as "Chuyuki" (The Diary of a Court Official) and "Meigetsuki" (Chronicle of the Bright Moon), and stories such as "Konjaku monogatari shu" (Tales of a Time Now Past), "Kokon chomon ju" (A collection of Tales Heard, Past and Present), "Heike monogatari" (Tale of the Heike), and "Ujishui monogatari" (Tales of the Uji Collection).
The position first appeared in around the 11th century when the samurai rank system was created, and it fulfilled the role of serving the household institution of court nobles, however, it ranked under Shodaibu (aristocracy lower than Kugyo) who would raise to Shii (Fourth Rank) or Goi (Fifth Rank), mainly placed at Rokui (Sixth Rank) (rarely, some rose to Goi). It is believed that the word 'Aozamurai' originated from the fact that costumes for those at Rokui rank were of hanada (medium blue); besides, based on the connotations of blue, that is to say "immature," 'Aozamurai' also meant a young or low ranking samurai.
In the late Medieval period, with the mandokoro (Administrative Office) and Ie no tsukasa (house steward) system that constituted mandokoro being broken up by the court, those of the court nobles at the level of vassals were to be reassigned to retainers, mainly including shodaibu and Aozamurai; however, the court nobles at the lower and middle levels who could not have vassals at shodaibu rank had only Aozamurai constituting their vassals and managing their households, whereas Aozamurai and vassals were treated as synonyms in some cases (according to "Noritoki Kyo ki" [The Diary of Noritoki YAMASHINA]). It was known that, in the Sengoku Period (Period of Warring States), when the Emperor or Sekkan (regents and advisers) was to issue hosho paper (edict paper) to make a command regarding low ranked people, the benkan (Council of State) who received the order commanded his own Aozamurai to issue the hosho paper, which was called Aozamurai hosho (according to the diaries "Chikanaga Kyo ki" [The Diary of Chikanaga KANROJI], "Nobutane Kyo ki [The Diary of Nobutane NAKANOMIKADO] and "Sanetaka ko ki" [The Diary of Sanetaka SANJONISHI]).