From the introduction:
In classical Japan, mythological shape-shifting animals help reattach the red string of fate between people who were meant to be together.
In Japanese folklore, it is believed that the gods tie a red string to the pinky fingers of people who are meant to be together. The red string may get entangled, contracted or stretched, but the lovers will always find each other. In rare cases, however, the obstacles are of such insurmountable magnitude that the string may get cut.