Zero, Leader of the Dark Matter Forces, was a great evil that had terrorized Pop Star and its solar system not just once, only to be defeated both times by a small pink puffball. Twilight Sparkle is a pony that has saved Equestria several times over. What do those two have in common?
When Zero was defeated the second and final time as Zero-Two, he was reincarnated as a pony with his power locked deep inside. Cadence said that Twilight was anything but a regular old unicorn when she was a filly, but nobody, not even Twilight herself, knew who she truly was.
But one day, everything that she knew about will change at the day of the Sonic Rainboom during her magic test. First there was Zero, then there was Zero-Two, and now, there is Zero-Three.
Gore tag is mainly for Zero's blood.