I am getting caught up and I think that the voice that gives Hibiki her power is the same as Root’s, but I am not 100% sure. I don’t remember any hints at all about who might own that voice from the WN during this sequence, and I didn’t read far enough to know the answer.

I am also in the same boat as you that I don’t remember Lancer getting powered up like this either. I hadn’t taken a close look at the character in the OP and thought that it might be Root they were showing. Root isn’t an adversary per se, but Makoto, Tomoe, and Mio sure view him as a threat to Makoto’s chastity, so there is that.