The Flame Imperator's eyes were cold as he pierced Yami's heart, but hidden in them was a wicked viciousness. His white flames were ready to overflow inside her body, and he wanted her last moments of life to be as painful as possible.
Venganza and Lucifer regained control over their bodies less than a second after the Flame Imperator sent them flying away, but it was already too late to help the Heavenly Empress.
Fury burned inside the heart of the Depravita of Revenge and the Champion of Justice and Order as they saw Yami's fate. Other than rage, there was also worry, as now that Yami was gone, they did not see a way they could keep fighting against the Flame Imperator.
Throughout their battle, the Flame Imperator recovered from the side-effect of Deceitful Reincarnation, growing much stronger. That is why he could neutralize Venganza and Lucifer and take care of Yami.