Farmer and Snake? but I Am Bound to the Xu Xian System

My name is Xu Fan. That day I picked up a strange frozen snake in the snow and almost roasted it and ate it. As a result, a "Xu Xian System" popped up, forcing me to save it. I was scared and stuffed it into my bed. Good guy, in the blink of an eye, black energy burst out. The snake turned into a big living person, and she was also a beautiful woman who was so cold that she fell into pieces. It also set me on the path of cultivating immortality