Columbina.
All the harbingers are occupied with their own matters/dead.
Pierro would not make an appearance, as the director, it is highly likely he'll be the last of the 10 who are remaining (10 because I included Pierro and see him as Harbinger number 0) that we get to meet. Even if there's a reason for Pierro to appear, he probably wouldn't. Columbina is the perfect candidate to be introduced as nobody else would be fit for the job unlike her.
As for what methods she could resort to, to me it would seem to be bargains, and only fighting if needed.
If not, I highly support of the idea that we will be given the pyro gnosis and that we might give it to tsaritsa or she would take it by force from us, whichever works.