Adja, a Slayer from the Gothic period of France, was sent through time to stop the demon Karfarnaum from assassinating Buffy Summers, a Slayer activated during the 20th century. Karfarnaum did not know which era Buffy lived in, but managed to pinpoint her location to Sunnydale, a small town that resided over a Hellmouth. The demon finally found Buffy in the year 2000, when she was a student at UC Sunnydale.
Adja caught up to Karfarnaum and intervened in time to save Buffy's life. Without the ability of being able to speak modern day English, Adja relied on Buffy's Watcher Giles to explain to Buffy that she was there to protect her. The presence of two Slayers confused Karfarnaum, who in its quest to kill Buffy, accidentally killed Adja instead. Adja's death triggered Karfarnaum's death as well, as the demon was only meant to live until it had completed its task - to kill the Slayer. Buffy later learned that Adja's people believed that Buffy was the savior of mankind and that Adja's only purpose had been to die so that she may live.
Her name, Adja, meant "one who is already dead". Adja called Buffy "Nasjands", which means "the Savior".