Not long before the events in Magic's Promise, Kaster married a woman named Ria. She was almost ready to give birth to their first child by the time Vanyel returned home to Forst Reach for a visit. Ria had been one of the women Treesa flung in Vanyel's path, hoping to turn him straight. However, Ria didn't appear to suffer any ill effects from her disappointment, and seemed relatively content with Kaster.
Kaster served as the righthand man of his older brother Mekeal, the Heir to Forst Reach. He was also Meke's accountant. Because of this, Vanyel appointed him Seneschal and Second Councillor to Tashir for the newly formed March of Lineas-Baires.