The Empire of Lethan is ethnically homogeneous in its dominant group of the Twi'Lek of whom have held the land controlled by the Empire of Lethan since their rise in Nord America centuries previously.
The upper and lower castes of Twi’lek society rarely mixed in social settings. The lesser castes stayed within the confines of poorer communities, choosing to keep to their own while the more noble castes busies themselves with political intrigues and/or amassing more wealth. The only instances in which the two might mix would be anything surrounding the Temple, as it is a central driving force within the Twi’lek culture.
The skin pigmintations of the Twi'Lek have historically been one of the main defining marks of who enters which caste. Certain of the ethnic groups of Twi'Lek have simply no ability to enter castes outside of their definded roles which is simply in the laws of the Empire of Lethan, with an example being Hulenia of whom are by law unable to enter Sesk'bumat, Sek'kesva, and Sesk'mahvus leading to the main reason behind the Hulenia being so marginalized.
- Sesk’bumat : The political caste. Members of this caste are koras, diplomats, and those who serve them such as attaches and assitants. This is considered a noble’s caste and its members are among the wealthiest in Twi’lek society.
- Sesk’kesva : The merchant caste. Members of this caste are craftsmen, shopkeepers, and others who engage in bartering or sales. This is considered a mid-range caste and its members usually make a comfortable living, although some of its members do manage to acquire considerable wealth.
- Sesk’mahvus : The Temple caste. Members of this caste are Tera’shi, Ai’jou and Kivas. This is the noblest of all castes due to the position of the temple in Twi’lek society. Its members are revered by all Twi’leks but make the meagerest of livings due to the vows of poverty their devotion to Kika’lekki requires.
- Sesk’nablin : The labor caste. Members of this caste are farmers, hard laborers, and miners. Its memebers do not have large incomes and are often plagued by health issues due to the difficult nature of their jobs. It is not uncommon for members of this caste to engage in the Vassij’ra.
- Sesk’osima : The artist caste. Members of this caste are dancers, musicians, poets and other entertainers. While members of this caste may be admired and revered for their talents, it is one of the poorer castes. Its members make meager livings and the Vassij’ra is not an uncommon practice for this lower caste.
- Sesk’ryvak : The medical caste. Members of this caste are doctors, medics, and other members of the medical community. This is considered a mid-range caste and its members usually make a comfortable living, although some of its members do manage to acquire considerable wealth.
- Sesk’vati : The warrior caste. Members of this caste are guards, hunters, military soldiers, and others who earn their livings through the use of arms. This is one of the poorer castes and its members make little money,often the Vassij’ra is used to increase wealth.