Kotaku is reporting that it is going to be Tsubaki Yayoi, one of the side characters that is prominently featured in Jin and Noel's stories.
Throughout the story she is mostly the soft-spoken older sister archetype, very diligent at school and always friendly. However, the main villain manipulates her into hunting down and killing both Jin and Noel. That story thread was mostly left in the air, until now that is.
Now, the big thing here is, that, well it seems a new version of the game is coming to arcades, tentatively titled Continuum Shift. Now, new arcade cabinet is all well and good, consumer's don't really feel that sting, but, here is hoping that they just bring this out as DLC for the home versions. Having several versions of Guilty Gear was painful but understandable enough in the days before DLC was standard. However, in this day and age, I do not think I could abide ARC releasing a whole new home version. At least without giving owners of the original the option to just grabbing the new content off of the web.
This is defiantly an ongoing story though, as it isn't fully known if Tsubaki is going to be in the European release of BlazBlue which has stated to have new characters in it. Will certainly be interesting to see how ARC goes about this.
Here is what she will look like in-game!
LOOK WHO CAME: