Sairou is the country protected by Byakko. Ruled by Emperor Nahido in Byakko Senki, it lies in the west and is composed largely of desert and ruins. Despite having Byakko as their Guardian God, it can be assumed that Sairou's people believe in more than one God since beliefs very similar to Buddhism spread widely in Sairou. This is the country where Tomo creates the illusion, the Tomo's City of Mirages. Later on, the illusion is repelled. It is associated with strength and challenge; represents soldiers fighting a war for their country's sake stands for the blooming season.
- Arudo: the capital city of Sairou. In Byakko Senki, he young and recently enthroned Emperor Nahido leads the country from there.
- Daijin Temple: a monastery led by Miboshi. Located to the south from Camp Ruins and to the west from Makan village. This place is suspected to be the temple where Chiriko, as well as Tatara dies in the hands of Seiryuu celestial warriors.
- A very similar temple is seen in the Byakko Senki manga, and it's the headquarters of the "Three Priests Alliance" cult.
- Nado Tribe: a village that was first introduced in Fushigi Yuugi Byakko Ibun, as it is the main village of the manga's pilot chapter. It is a border village near to Kutou and the villagers were known to fear spellcasters and shape-shifters to the point of violent persecution. Reipin, known as Neiran, hails from this tribe.
- Tomo's City of Mirages: an illusional town, created by Tomo in the middle of Sairou to distract Suzaku celestial warriors.
- Makan Village: the village where Amiboshi, a Celestial Warrior of Seiryuu lived after he fell into a river in Konan and lost his memories in the original series.
- Camp Ruins: an exclusive location in Fushigi Yuugi DS and Fushigi Yuugi Suzaku Ibun. Located to the north of Makan Village, this has to be visited in order to acquire the "Staying Behind" ending of the game.
Rather contradicting the other three countries, Sairou's climate is extremely hot. The terrain is comprised of mostly sweeping deserts, deep sandstone trenches, and Middle Eastern-style housing.
Sairou's geography seems to be inspired by the Silk Road, the famous land route connecting Europe, the Middle East and Asia. It was once stated by Tasuki that a person can only go out in the night or else "the sun will toast" him.
- The people's pluristic beliefs allowed the growth of a powerful cult known as the Sanga (Three Priests Alliance), which is led by a mysterious man known as the "Great Priest." Nahido and the Arudo authorities fear that this will cause a schism and destroy the country.