Void Manifestation didn't just give Bai Yumo's mana the properties of the Void, but gave him a portion of the Abyss itself.
The mana transformed from his own wasn't any different from the Abyss's Source Mana, something beyond his control.
Every time he used Void Manifestation, a portion of his ego was consumed by the Abyss, so he was forced to find other methods to fight.
Under the Saint Emperor's guidance, these methods became perfect copies of Damien's own, which, in its own way, killed his ego further.
However…
'No. I cannot use that until the time is right.'
If he couldn't use "that," then his only option was Void Manifestation's final trump card.
The question was: if he used it, would he live to accomplish his ambitions?
'But if I don't use it, I will die here today.'
He didn't have any other choice.
He realized this earlier, but it finally sank in when he saw Damien coming towards him now.