Yu-Gi-Oh! 5D's - Season 1 Episode 146 The Last Human , Z-One

With the 3rd gear stopped, the Signers gain access to the Center Gear, and Yusei rejoins the others, telling them the truth about Antinomy, and about the Delta Accel Synchro method. They continue onwards to the center of the Ark Cradle, where they spot more, but smaller gears, as well as the Ener-D Generator that was called the Center Gear, which was powering most of the negative Ener-D of the Ark Cradle. Then, they enter a room with blue walls, located at the very heart of the Ark Cradle, where ZONE awaits them. Z-ONE reveals he was behind the Zero Reverse incident, as well as Paradox's scheme, to try to stop the existence of Synchro Monsters, and Ener-D. Z-ONE then decides to settle things in a duel, and if Yusei wins, the Center Gear would stop working (the Center Gear is really the key Ener-D generator, which is the main source of power for the Ark Cradle's overall Ener-D Generator), and the Ark Cradle would disappear for real.