System No. XX

System No. XX is the main antagonist of BlazBlue: Cross Tag Battle.

Information
System No. XX was created by Clavis Alucard, Rachel Alucard's father. Originally, she was designed to create new possibilities. However, there was a flaw in its design: The machine has invaded the world she observes and used them as power bases. Fortunately, Clavis sealed the system away using the keystones of the selected universes: BlazBlue, Persona 4: Arena, Under Night In-Birth, and RWBY.

But, the seal was accidentally undone by Rachel, releasing the system in a process so that she can summon warriors from those four universes and having them fight in Tag Battles to participate in the "Keystones Tag Battle Tournament" inside the Phantom Field, telling the warriors such as Ragna the Bloodedge lies as they need to collect 4 keystones in order to escape and go back home to their respective universes.