If Fuyumi Ono made an entire series devoted to covering Shoryu and Rokuta over the 500-year period of the Ever-King's reign, I would import them and then rebuy the books should they be published in English. The Twelve Kingdoms: The Vast Spread of the Seas is addicting that way, centered on delivering overblown fights over the roles of kings with manuvering by very important and intelligent people.
This story also has the benefit of not coming across as an afterthought like it does in the anime adaption, as well as avoiding the awkward attempt at a frame tale to preserve Yoko as the main character.
What is distressing, though, is the current lack of availability here. Probably just a short print run by Tokyopop, knowing the economy and their situation, but it's still not satisfying.