Two opposing lines of thought.

First, he's referencing Minfilia's soul. Could be seeing the Word of the Mother traits, or Venat in her. Or he could be recognizing that fact that hers soul functions similar to an Ascians and believes that could be the start of a common frame of reference between the WoL's group and himself.

Second, he's recognizing the WoL's souls as possibly the 14th member of the Convocation and that they were originally female.