Is the TBB Rasengan training preparing Naruto to learn sage mode + RKS mode fusion?
Something that's bothered me about fusing sage mode with RKS (Rikodou Sennin) mode is that while in RKS mode, Naruto is exchanging his yin and yang chakra for the fox's yang chakra alone, as the yin was sealed in the belly of the death god by Minato.
Thus, if Naruto starts in RKS mode and draws in nature chakra, he would be half yang Kyuubi, 25% yang nature, and 25% yin nature. As I understand it, this would not be balanced since he'd have 75% yang and 25% yin.
TBB Rasengan training balancing light and dark:
Now, Naruto is training to make the TBB Rasengan using a specific ratio of black and white Kyuubi yang chakra ( I believe he's aiming for a 8:2 ratio, but I forget).
Achieving yin and yang balance in sage RKS fusion mode:
If Naruto were to apply the same principle to nature chakra he could draw in only yin nature chakra, which would allow perfect 50% yin/yang. But the nature chakra might not enhance the Kyuubi yang chakra Alternatively, if he drew in a ratio of 2:1 yin:yang nature chakra he would have a perfect balance of yin and yang, and his yang would be composed of both Kyuubi and nature chakra.
I don't know if this can be done, but I'm curious what other people think.
1.) Namely, is Kishimoto using the TBB in part to foreshadow sage/RKS fusion?
2.) Will it be necessary for Naruto to draw in nature chakra in a specific yin/yang ratio to fuse sage and RKS mode?