Hmm, just updating with more changes I am considering...
1. The Oni are master manipulators, why not have them stoke Prince Batsaikhar's desire for one of the NPCs (or PCs), and stage an ambush on the last day of the feast after he has been turned down? A stand-off of sorts with a level appropriate encounter of Ordu-Aganhei's finest (mostly mooks, Batsaikhar is a bit of a blow-hard, but with the bodyguard Izume being a legitimate threat).
2. With the slightly reduced role of Miyaro as a guide to the forest of spirits, and the possibly increased role of the ninjas in the Tide of Honor book, perhaps she could be the daughter of the Ninja Grandmaster? In which case, her interference would be non-lethal, as she strives to subdue her wayward brother/sister ninja, before the party kills them. PCs who can speak Tien hear the ninjas refer to her as Ojou-sama before they are knocked unconscious.
3. Seranrae is the goddess of mercy and compassion, why not make the dark oni blood of the PC (Norrin Shee, the paladin of Seranrae) part of a redemptive story? The half-fiend daughter of Anamurumon could clash with the Emir Saladin, attempting to free her father, only to be redeemed by his/Seranrae's compassion. They wed, and the tainted blood flows within the bloodline of the leader of the "Warriors of the Sun"
Even more reason for the native Minkaiains to be suspicious of them! (leading to Emperor Shigure to order a purge of their numbers, a purge that Anamurumon, in his guise as first minister, was more than happy to carry out)
a: They are strange foreigners.
b: They practice a sun worshipping religion that is distinctly not Shizuru, the heretics!
c: Their leadership is said to have demonic features!
and of course d: They are powerful warriors and might be a powerful faction that opposes the throne of Minkai, it doesn't help that they seem to adhere to their own agenda (oni slaying) that sets them apart from the rest of Minkai.
As usual, I am interested to hear your thoughts.