Either Villagillo or Moid
After all, the Vox units are practically fueled on the stuff, and that certainly amplifies between the three pilots. The WHATEVER THE HELL Vox Aura
did was certainly within anybody's evil intentions. It's likely Villagilio did his best to break Muginami
with full intent to make the other two Vox units do the same thing.
- And Not-Kotetsu is Simon.
The Vox were...
Originally made to terraform planets but the pilots lost control and ended up destroying most of civilization on Earth at the time. The true nature of the units were lost to history out of fear towards their power until they are used as they're supposed to at the end of the series.