The Energy Amplifier is a cylindrical weapon stored onboard the Ironclad. When Blackout turned Darkmount into a giant robot body, Kakamu took the Amplifier from the Ironclad, went Nova, and poured his Nova energy into it. The stored Nova energy inside was amplified and fired out of the other end of the weapon as a large beam of energy, which went straight through the robot's head. As a result, Blackout had to resort to using his original body again, while Kakamu's original body perished, leaving only his consciousness intact.
It may or may not be related to Naterohk's Elemental Amplifier.