While Damien was within Lily and Mei's spiritual world, the situation on the outside had also calmed down.
Since the girls weren't fighting, their mana also stopped responding. That's how it should've been since the beginning.
And as they worked together to balance their spiritual world, Damien put in the work to help them balance their body.
His Void Essence wall split into countless threads that went forth and enveloped all the mana within Lily and Mei's body. Considering how much vaster his capacity was compared to hers, it wasn't too hard.
And then, he used a property of Void Essence that he had never used on someone other than himself. He brought the two different forms of mana together and used Void Essence as a bridge to fuse them.
The reddish-black and blueish-white mana wrapped around either other like a yin-yang symbol, but there was still a wall of Void Essence in between.