The Qi of Yin and Yang is the inherent "Qi" possessed by all male and female creatures, including humans.
Among humans, males are born with "Yang Qi," while females are born with "Yin Qi."
"According to the information inside the jade slip: near the entrance of this small world, whenever a creature carrying 'Yang Qi' and a creature carrying 'Yin Qi' come within a thousand meters of each other, spatial turbulence will appear and sweep them both into the small world..."
Chapter 2586