@Purple:
I was thinking either it was the queen's people because they're setting up for an invasion of kanyou on Sei's rise, but Ryofui is also an equally good option
That's not a bad idea, but it doesn't make a lot of sense to me story wise. We've had no indication that the queen knows of the relationship between Sei and the Hi Shin Unit, and keeping that in mind what would the Hi Shin losing a battle accomplish for the Queen? Not being able to take that one city might allow the Wei to push back to Tou might have to spread out his forces more or they might need more reinforcements giving the Queen a better chance to attack, but it just feels like an extremely specific plan for her to then randomly choose the one unit in the whole army that has a special relationship to her son. I dunno to much of a coincidence if thats how it is.