I don't think many people know this, but there's a 5-volume light novel series that was written after the end of the manga series as a side story. These novels are all set about 10 years before the beginning of the manga series and detail the childhood adventures of Kail and his brothers and friends, often battling against the schemes of his stepmother Nakia. Unfortunately, Yuri doesn't appear in any of the novels, but on the other hand it's all new material, unlike the light novel adaptions of other series which just retell the original story in book form. I have scanned the first 3 volumes because I bought 2 copies of each while I was in Japan. Perhaps I can get a second copy of the last 2 volumes when I get back to Japan, in which case I will scan the last two volumes as well.
Volume 1 - Ma ga Toki no Reimei
Suspicious of the circumstances of his mother Empress Hinti's death, Prince Kail recruits his younger brother Zananza to investigate. They begin to uncover the plot of a priestess named Nakia, who is aiming to become the next empress, but they have no proof. Furthermore, the hand of evil is closing in on Zananza...
Volume 2 - Zoku - Ma ga Toki no Reimei
Conclusion to the events of the previous novel.
Volume 3 - Tsuitachi no Tsuki
Kail met with the brother and sister Kash and Tessa on his way back to the capital. While suffering under the burden of their sick mother's property taxes, the two former aristocrats have not lost their pride. At that time, the son of the official governing their village started demanding the sister, Tessa, become his concubine. However she's become enchanted with Kail, not knowing that he's the prince of the Hittite empire. Kail has also become fond of courageous Tessa...?!