Khun Agnis (쿤 아그니스, Khun Ageunis;) is the biological Mother of Khun Aguero Agnis. Agnis is actually a family name, her first name is still unknown. She had a younger sister who was killed in a fight between families. Her younger sister is Khun Kiseia's mother. After her sister was killed, she adopted Kiseia to become Khun AA's foster sister.
A fans asked SIU why AA's mother look ugly in the Part 1, then SIU responded that Khun Agnis is actually a great beauty and Khun Aguero Agnis resembles her. She looked ugly in the Part 1 because SIU drew her that way; but in reality, she is a wife of a House head, so of course she is not ugly haha.
Kiseia's Mother is her biological sister. So Kiseia is her niece. After her sister died, Agnis adopted Kiseia to become Khun AA's foster sister.