Following is a short list of ideas and premise used in this story. Please read it before starting on the story. It will make more sense.
Sesshoumaru and Kureha had studied together since they were children.
Kureha's mother and Inu no Taishou had an alliance against a foreign youkai invasion, and since then their kin kept their alliance.
Kureha was entrusted to Sesshoumaru's mother while she received lessons from sages gathered at Sesshoumaru's mother's palace.
They met every few years, and Kureha stayed about half a year each time.
Kureha's Orochi (Great Serpent) clan and Sesshoumaru's Inu Daiyoukai have different customs and social structure.
Youkai do not have convention of marriage.
In my universe, Inupop was an absent father. He did not live with Sessmom, and he visited Sessmom and Sesshoumaru from time to time, occasionally giving Sesshoumaru lessons when he was around. (as seen in <A Href="https://www.deviantart.com/deviation/47400126">