When one Slayer Dies , another is sent to take her place. When Buffy Died in series One The watchers Sent Kendra to the Hell mouth to take her Place. Unknowing that Buffy was brought back to life by Xander and Angel. After everything was cleared up with the Kendra mix up she returned to her Watcher. Soon though it was called for Kendra to come back and help Buffy, Kendra was killed by the Vampire Dru. Another Slayer wondered onto the scenes , Faith , after her watcher was killed she came to Sunnydale where she later killed the Vampire that had taken her Watchers Life, with some help from Buffy and then stayed to train under the watch of Giles. But later in the series it is shown whos side Faith is really on and she pays the price for messing with Buffy!

Buffy and Kendra Faith