A very short parody (well, sort of) of the 'marriage/concubine/whatever contract' trope.
Willow wants to give Xander what he deserves. Rating is for later chapters, which will contain explicit sex, among other things. Updates may be very slow.
The One Who Screws Up Prophecies is given the Gift of Knowledge... without needing to pay an eye for it. Rating is for later parts, in which Xander gains a harem.