Jasei no In: The Serpent's Lust is a short, linear game with a strong narrative. It tells a story adapted from a Japanese classic collection of supernatural and paranormal stories called Ugetsu Monogatari. This particular story is a very popular one in Japan, and has gone through many adaptations since its initial creation around 1776.

The protagonist, Manago, is a simple weaver girl who gets caught in a rainstorm. A mysterious man in white appears out of nowhere and shields her from the rain, lending her an umbrella. Feeling indebted to him and perhaps a little attracted to him as well, she tries to return the umbrella to his manor hidden deep in the woods. Manago quickly becomes swept up in a romance that is not all that it seems, and must figure out who exactly the mysterious man in white really is, or face severe consequences.