Canto IX boss

I think I have an Idea of who the final boss of the Canto is gonna be, but first let me explain my thought process:

First I though it was gonna be one of the nursefathers (mainly Rien) or some sort of "Doctorgrandfather" that lead the entire house of spiders "cough" Horikawa "cough".

I also briefly though it was gonna be all 5 apprentices at once before I dismissed it.

It couldnt be all 5 Nursefathers, that would be impossible to win (at least without Vespa's help, and I think having Vespa by our side would make the battle less about Ryoshu).

But then part 2 released and:

1: If there was some sort of "master of the house of spiders" at this point we would have heard about them already.

2: We fought a nursefather, and while powerful she did not have the Flashyness typical of all Canto final Bosses post Ahab, and her HP was only 1918, and aside from the apple and Kromer (and Ahab if you do not add up the Hp of all of her phases) this is less than all Canto final bosses.

So my running theory is that the final boss is gonna be Araya, having been turned into the "blade that cuts through all" that they wanted Ryoshu to be using N-corp tech.