An Extradimensional Terrible-Being created by Yapool to defeat Ultraman Ace. Ace-Killer can use all of the special attacks that it stole from the four Ultra Brothers.

The four Ultra Brothers were taken as a prisoner on Planet Golgotha in a negative space after falling for one of Yapool’s schemes. Ace-Killer arrived so Yapool could transfer their abilities into it. Then, Yapool made Ace-Killer fight against a robot imitation of Ultraman Ace to test its strength and Ace-Killer destroyed the robot with ease.

Next, Ace-Killer fought against Ultraman Ace after Ace arrived on Planet Golgotha. Shrugging off a Metalium Beam, Ace-Killer unleashed a barrage of the attacks he stole from the Ultra Brothers, overpowering Ace with a barrage of Spacium and Emerium Beam attacks. However, Ace received the Ultra Brothers’ remaining energy allowing him to turn the tide of the battle, and Ace-Killer was disintegrated by Ace’s Space Q attack.