Ucinaasugai (Okinawan: ウチナースガイ/沖繩姿), also known as Ryusou (Japanese: 琉装りゅうそう, also written as ryusō) and referred as ushinchi in Okinawan, is the folk costume of Ryukyuan. Ryusou is a form of formal attire; it is customary to wear it on occasions such as wedding ceremony and the coming-of-age ceremony. The ryusou became popular during the Ryukyu Kingdom period. It was originally worn by the members of the royal family and by the nobles of Ryukyu Kingdom. The Ryukyu Kingdom was originally an independent nation which established trade relationship with many countries in Southeast Asia (Java, Malacca, and Palembang) and East Asia; they held their relationship with China as especially important. The development of the ryusou was influenced by both the hanfu and the kimono, demonstrating a combination of Chinese and Japanese influences along with local originality.

The ryusou shows a combination of Chinese and Japanese influences as well as local, native originality. Robes which crossed in the front was worn by both the working and upper classes; however, they differed in length (from knee to ankle length). The working class would wear a knee-length robe while the upper classes would wear robes which were ankle-length.

During the Ryukyu Kingdom period, the colour, fabric, and design of the ryusou, alongside the style of headgear, was used to distinguish the social status and rank of the wearer.

Men's ryusou differ from women's ryusou in terms of colour, design, and material. Men would secure their robes with a sash or girdle but women would hold theirs with a pin. The ryusou for women is based on the bingata (紅型, lit. 'red patterns') style of dyework. Bingata could only be afforded by the people who had a rank and were wealthy. Bingata textiles were strictly supervised by the royal court. It was closely associated with the royal court and was traditionally reserved for the royalty of Ryukyu and aristocrats, and for warrior families. Bingata is brightly-coloured, commonly using red dye derived from cinnabar, the most important colour in bingata, imported from Fujian, China. It is also suggested by Japanese scholar Yoshitaro Kamakura that the dyeing and painting techniques, styles, materials, motifs (e.g. Fujian-style Chinese bird and flower were introduced under the reign of King Shō Kei) of bingata were also imported from Fujian.

A form of ryusou for women is intended to be shorter than the kimono: it is a two-piece garment attire which consists of dujin (胴衣; ドゥジン; cross-collar upper body garment) and kakan (裙; カカン; a pleated skirt). A woven or bingata garment, called watansu (綿御衣; ワタンス), can also be worn loosely over the dujin and kakan. Only men of royalty and from the warring class were allowed to wear dujin and trousers as an undergarment.

Ryusou can be made of high-quality plain-weave hemp fabric called jōfu, and bashōfu (芭蕉布), which is banana fibre textile. Bashōfu was the preferred textile for summer due to its airiness, for its smooth surface and because it does not stick to the skin in hot weather, making it suitable for the hot climate of Okinawa. According to the Zhongshan chuanxin lu (Records on Chûzan), bashōfu was worn by both men and women during winter and summer, and its value equalled that of silk. Bashōfu was also used in the making of official garments, according the Ōshima hikki (大島筆記) written in the 18th century by Japanese Confucian Tobe Yoshihiro.

Due to the differences in climate and culture, Ryukyuan clothing differed to that worn on Japan. Compared to the kimono, the ryusou has big sleeve openings, which allows for good air circulation to keep its wearer cool in tropical weather. The ryusou also uses a thin waistband instead of the wider obi worn with the kimono. The ryusou is also very light, mobile and loosely-tailored compared to the kimono. The ryusou is generally shorter than the kimono.

Cotton was exported to the Ryukyuan Kingdom as early as 219 BC from China. The Ryukyuans appear to have started weaving around the time there was initial contact with China, most likely during the Han dynasty. In the Yuraiki, under the entry Ori (織, lit. 'weaving'), it states that "It is not clear when weaving began in our country. This was probably from the time that there was contact with Han [China]".