BlazBlue: Phase 0 is a light novel written by Mako Komao and published by Fujimi Shobo that was released on August 20, 2010. There has been no word on an official English translation of the novel.
A short manga and a Drama CD based off Phase 0 were released as pre-order bonuses alongside BlazBlue: Continuum Shift II for Nintendo 3DS and PSP. Both focused on chapters from the beginning of the book, but did not show the whole story.
The novelization that spins the tale of the origin: Phase 0. Phase 0 is an official light novel that will focus on the secret battle between Ragna the Bloodedge/Bloodedge and the Black Beast. The Black Beast, the Six Heroes, the Alucard Family, the Takamagahara System, and the many mysteries of the Azure intersect, connecting to the Origin of the BlazBlue series. When a young lady harboring a mysterious power, Celica, has a chance encounter with Ragna, the door to the origin of the BlazBlue series, Phase 0, opens.