The Eight Coloured Sages (彩八仙 Sai Hassen) are immortal spiritual beings. The Immortals make appearances throughout the anime and light novels but are rarely seen together.
They were said to have aided the warrior Sou Gen to drive away the demons that infested his country.
Sou Gen went on to found the nation of Saiunkoku and became its first emperor. After Sou Gen's death, the eight sages disappeared, but according to legend they still exist among the people. A beautiful shrine was built for the Eight Coloured Sages and still stands within the Imperial Palace.
To honour the Eight Immortals, Saiunkoku was divided into eight provinces, each named after one of the Immortals and for its ruling clan to be named after the province it ruled.
The Coloured Immortals have resided in or taken the form of humans in order to observe the people of Saiunkoku, rarely interfering directly. However, their interactions with other humans may influence the outcome of major events that occur within Saiunkoku.
Took on the identity of Kou Shoukun, the Rose Princess of the Hyou Clan. As the Rose Princess, she was known to have possessed a number of supernatural powers. She eventually married Kou Shouka and had a daughter, Kou Shuurei. After giving birth to her daughter, a number of her powers diminished due to using up most of her vessel's life force, except the ability to keep her host alive by remaining dormant until the day of his or her natural death.. When she utilized this power to cure her daughter from illness, the Red Immortal's spirit resides within Shuurei's body and remains dormant to keep her daughter alive. She is one of the strongest among the Immortals.
Resides within the body of Ran Ryuuren, the fifth son of the Ran Clan who lives as an itinerant. The Blue Immortal possesses his own separate consciousness from Ran Ryuuren, leaving Ryuuren unaware of his status as the host of the Blue Immortal. The Blue Immortal is called the Lord of Time, who rules past, present and future.
Took on the identity of Sho Yosei, one of the Grand Advisors to the current Emperor of Saiunkoku. Despite his status as one of the emperor's advisors, he does not serve the country for its own sake and is only loyal to a worthy emperor. His actual name is Shi Shou. He is the strongest among the Immortals.
Resides within Ouyou Jun, a member of the Heki Clan. He is married to Heki Karin, the next head of the Heki Clan. The Green Immortal is sharing the body with Jun to sustain his life force like Byakuya and Eigetsu.
The White Immortal resides within the body of Tou Eigetsu and manifests himself as Eigetsu's alternate personality, Yougetsu. Prior to this, he did not have a host body and is currently in a deep sleep to sustain Eigetsu's life force. His actual name is Haku Byakuya. He is one of the strongest among the Immortals.
The Black Immortal is called the Lord of Twilight, who rules the boundary between life and death. He is considered to be on par with Shi Shou.
Took on the identity of Nan, Ro Ensei's martial arts master.