Oh wow, I missed this, apparently. Beige jacket fight?
It can actually be done pre-slight rework of his page, too, since the final key's essentially going unchanged. Hopefully this isn't a Necro.
I guess I vote mah boi, for reasons above, though I can also elaborate on some specific bits with one of my signature essays-
As it stands, for starters, I see no reason that Zain doesn't also automatically have all of Saeko's powers on account of her being a sapient entity, in combination with the True Monad's archetypical nature as 'all sapient entities', unless I guess you want to rule that's an 'assimilation' power of sorts that she can resist? Even if Saeko isn't just a part of the True Monad on account of what the True Monad is, you're looking at an infinite wall of everything that a sapient being can do with Allbring for an opening move, an unlimited well of willpower to defend against anything that can be thought of as a 'Reality Fracture' which at this point is more or less anything that is a threat to the existence of sapient life, i.e. him,... etc.
He has multiple feats of using the Sephira to resist hax above his paygrade even before receiving the Kether proper, and even following that withstood witnessing the Ain Soph Aur (i.e. the twelfth "Sphere" of reality that holds apart the Tree of Life from the rest of the world, effectively preventing anything higher than 12-D from interacting with anything within it for fear of the whole cosmology falling apart like it almost did the first time), so... I don't really see any of the hax she has working any time soon.
In theory, that scythe might be a Win-Con, since hax in her world seems to reach High 1-B levels to some degree? But assuming that it can shut off the Tiphareth, even, the likelihood of her actually getting something like that off against, y'know, someone that wields the duality a hit off against someone with that kind of sheer defense isn't great. Plus, you know, "...Her scythe can only control humans and it can't control people if they have a strong enough will, love trumps it's influence, a lack of emotions or an immunity to pain also prevents the scythe from controlling them." seems like a pretty debilitating weakness against a character whose superpower is the perseverance of the human heart made incarnate.
Eyes of the Observer would be a trump card, except the Daathe exists on top of the Kether. The whole point of Arc IV and the Daathe, etc. is that "it doesn't really matter whether or not something can be categorized as 'real' or not, my ascribing meaning to it as a conscious being with thoughts and hopes is enough to make the difference meaningless"- in order words, deciding something Zain does or is isn't 'real' isn't really going to make a difference here. This applies on an infinite scale, an account of the Kether... you see where this is going.
Basically what I'm seeing: Saeko makes Zain into Waifu Zain, who proceeds to say "lolokay, I Allbring with all-of-life-plus-you's powers, to prevent any wall of hax/resistance you might have to stop me from Sealing with Ahura Mazda before that scythe gets anywhere near me just to be on the safe side." (Of course, convincing her to stop fighting with Talk No Jutsu'd be preferable in-character, but somehow I doubt that goes anywhere, his mindhax/social influence feats aren't very impressive.)
I guess I'll wait for Round 2 to see if anything changes...