When we were first introduced to the Buffy character, she was an only child and she remained that way for quite a while. However, Dawn, Buffy’s sister was suddenly introduced into the Buffyverse. She was not born a baby girl; in fact she's supposed to be just a few years younger than Buffy. Later it was revealed that Dawn is not in fact a normal human being, but a physical shape given to a mystical device called “the key”. This key is supposed to be a catalyzer that enables the bridge between dimensions. A group of wise monks created the human form of Dawn to hide the Key from the reach of Glory (an evil goddess) who was trying to create an entryway to her home dimension. If she succeeded in creating this portal then the structures that separate earth from hellish universes would be torn down resulting in the destruction of reality as we know it. Of course, Buffy stops this from happening, but sacrifices herself in the process.

Dawn is first presented as a troubled teenage who has a hard time dealing with her sister's role as a Slayer. She is the cause of some trouble as Buffy finds herself in constant need to save her from dangerous situations some of which she brought upon herself. She becomes a kleptomaniac and she runs off with questionable and sometimes undead crowd. She falls in love with Spike for a short while and with Xander too.

As Dawn matures and tragedy keeps happening around her household (the death of Joyce and the second death of Buffy) she becomes an extra ally, helping the Scooby Gang with research, mostly. Most importantly, she remains Buffy's emotional support and stands by her side when Angel and Spike are no longer with her.

Recently since the destruction of Sunnydale Dawn has gone to College. There she met Kenny and she had a relationship with him. But she cheated on him with his room mate and she was magically turned into a giant. One of the two men is a Thwice altough which one it is sin't revealed yet

Dawn now lives in a castle in Scotland with the Scooby Gang and all of the other slayers. She has only revealed the origin of her size to Xander.

Dawn's size gives super human strength but it is below normal for her size. It is also possible that Dawn might still be growing.