Re: Yin-Yang Release (陰陽遁, Onmyōton) Training.
From my research, each type of chakra interacts with different levels of the mind, body and spirit.
Originally Posted by Xylon
This one (Solar Plexus Chakra) is related to one's self esteem, will power and motivation.
Now quoting from the source ''It is the most crucial energy centre to concentrate on to ensure our ability to create a happy, satisfying life.''. So i guess that will power and motivation are essential for us to achieve our objectives in life and thus, achieve happiness and a satisfying life.
From my point of view, our ambition comes from it and our desires and objectives can only be realized thanks to that chakra. Our will to achieve something we want in order to feel happy (at least, i think that is the main reason why we do something, to feel happy with ourselves, even if other people thing we're doing something wrong)
In conclusion, it seems it is a kind of positive chakra so i would relate it with the Yang side, tough i'm not sure if that's what you wanted when you asked to relate to the Naruto Universe
Edit: And just like Yin-Yang, it has it's opposite side, which would be low self esteem and negativity with ourselves, like feeling we can't accomplish nothing so we just quit. That way, we won't be able to achieve a happy life since we don't ''make our dreams come true''. So that would be the Yin side.