The southernmost kingdom of the twelve, bordering the Red Sea, the kingdom of Sou is one of the four "central" kingdoms. Its king is known by the appellation of Priest-King.
The Priest-King of Sou currently holds the oldest living reign, at 600 years, of the all the current kings of the Twelve Kingdoms and holds the second longest reign in the Twelve Kingdoms’ recorded history. The king and Sou's kirin are never formally introduced in the anime series. Enki describes the king is a meikun (名君, "great ruler") and states that the Kingdom of Sou is prosperous and tranquil under his rule.
The family of the king of Sou helps to run the country, and is actively involved in social improvement projects, as mentioned by Shushou and Rakushun. The prince of Sou,Ritatsu, assists the king while the princess of Sou, Bunki, created a national hospital where many patients are treated. She is credited for providing Sou's health care. One prince, Rikou, appears in Tonan no Tsubasa and the short story Kizan, where he and Shouryuu (under his alias Fuukan) run into each other in the falling kingdom of Ryuu.