Dawn Summers, 15, is The Key, and Buffy's sister. After protecting The Key for centuries, the monks of the order of Dagon were forced to hide it from Glory by turning it into a human girl. They placed Dawn with the Slayer, disguised as a younger sister, and implanted memories in everyone in Buffy and Dawn's lives that made it seem as if Dawn had always been a part of Buffy's family. It is unclear how the implanted memories are activated or if people outside of the Summers' lives know about Dawn. The insane and those "outside of reality," such as clairvoyants, are able to see that she is not real, and Buffy was able to identify her as part of a spell by going into a deep trance. Joyce seemed to recognize that Dawn was not her daughter at certain moments when she was being affected by her brain tumor. Dawn was initially unaware of her true nature, but learnt the truth, much to her distress, when she broke into the Magic Box and read Giles' diary. Glory's aim in this world was to find the Key � it turned out the Key could break down all the dimensional barriers, and Glory intended to use Dawn in a ritual to get back to her own dimension. This ritual would result in Dawn's death, and the unleashing of countless demon dimensions on earth. Buffy wasn't able to stop Glory from starting the ritual, but by sacrificing her own life she was able to stop it in time to save Dawn and the world.