Is it really necessary? I think you were making a good point about them working together.
I am not sure about their loyalty to Natsume (they seem to be somewhat disgusted by Aya's penchant for mental torture), but they do seem to be working in tandem.
I wonder whether the present world Kabane and Shoujou are working for someone, or they are just together because of many-generational friendship of their families?
Oh, and by the way, regarding the True Warrior. I was checking out the two girls back in volume 14 and it seems like you were correct, kk1, it was already confirmed earlier. Not outright, but rather clearly. Here's a quote:
Kabane wrote:"Power" can usually only be applied in one direction...
That pressure is brittle when attacked on the flank. And the bigger the "power" the bigger those "weak points" are going to become.
A long time ago, in order to cover for the deficiencies in those weaknessess, the Takayanagi blood was split up amoung the twelve founding families.
For example, for this - ... "Dragon's Eye" which can consume an unlimited supply of "ki", there was the "Dragon's Fist" which can collect and supply huge amounts of ki.
So, the question will now be: Is Inue lying to Nagi about him becoming the True Warrior, or is Kabane misinformed about the origin of the Families? Or perhaps the title of the True Warrior can change hands based on whoever possesses all the powers of the Twelve Families? The latter seems rather probable.
Now, too bad our hopes for Masataka are quenched so easily. No way he can outdo Nagi in combining the Red and White powers...