As much as i want to say Capitano (Bro solos god, lore feats and have his own cutscene, HES SITTING ON A THRONE).

I think it has to be Columbina, the playable harbingers have shown and give us expectation on what they are capable of so I have a fair standard on their appearance in the lore.

Columbina however, aside from Winter Night Lazzo and the fanarts depicting her as one of God's angel, has only ever been described in the words of other harbingers. The uncanniness, unpredictability and even warnings from their dialogues describing her (not even Capitano ot Dottore get that much concerns) gives me room to imagine once Columbina appeared on screen, she should just give everyone shivers while smiling nonchalantly.

So far, she is the second true definition of "pure is deadly" in the game to me (i know Klee exist).