Tsunade's chakra nature is Yin. Nagato's chakra nature was Yin Yang. Sage of the Six Paths chakra nature was Yin Yang...
She does have an affinity which is presumed to be lightning due to her ability to rapidly turn chackra into electricity without making any hand seals. However, if your Chakra nature is Yin you can turn your chakra into many elements. Fact that only element that could work inside the body, that's why she used electricity... she's the greatest medical ninja of all times, therefore she would use elements that would boots her medical prowess.
Yin chakra controls life while Yang controls Death. That's why Nagato's rinnengan was said to control life and Death while Tsunade's Yin seal gives her Immortality.
Yin chakra is CREATION , Yang chakra is devastation.===== Tsunade uses CREATION rebirth====== Nagato uses Planetary DEVASTATION.
It's a Japanese thing... you can go and research for Yin and Yang.
Hope I was helpful.
Last edited by Slug Princess; 12-31-2012 at 04:21 AM.