Story idea, up for grabs

Xander, somehow sent back in time to before America was discovered as the New World, gets taken in by a native tribe and is witness to the beginning of the colonization of america. While living as part of the tribe, "married" to the Chief's eldest sone, he discovers something that the Watchers have fought to keep secret for generations; that there were slayers among the native americans that were killed before being called in order to keep the line of slayers in "control", as they so nicely put it.