So you can learn Tao by hand-holding, the screwing part is completely unnecessary.
It didn't look like those "I have reason!" monsters were so worried about Mei for the sake of other monsters, they were totally planning to use her for themselves.
You can also learn Tao by eating humans that turned into plant (Ten) but I suppose that would be a crime in their society.
It's one sect of Taoist belief that you could cultivate through intercourse. Cultivation is a common concept in Chinese myth and Xianxia stories. It's a system that seemingly has no limit in how much stronger you can become.