...okay, back on topic, I feel probably legally obligated to try to drum up a good argument for mah boi (incoming text wall, be warned)-
Even with transformation into Ice Armor/Wyvern Form off the table (see: it's 7-A and Low 6-B, respectively), Taiga is really strong for Zain at this point in the story. She seems to have more types of elemental attacks, for starters, and the Glyphs probably help to counter his Zone Control somewhat. Her magic is sitting at ~3.82 Kilotons at base next to Zain's ~3.7 Kilotons, which while not exactly very big is at least probably worth noticing. She also in all likelihood has better telekinesis, since Zain's at this point mostly just consists of doing fancy sword throws for combos and such.
As far as general training, from what I can glean of Taiga's profile, she's probably at least on an even keel at around the time she's 17, maybe somewhat less skilled/experienced but not to a major degree. Zain's 20, and has been at least training to do this sort of thing for a decent chunk of his life now, but three consecutive years being trained for combat in that way. Both have Gifted for Intelligence, kilometers for range, the same slight Regenerationn...
Zain's Fate Break is scary-looking, sure, and technically speaking 9-dimensional, but it's more an anti-hax than anything: probably of little consequence in this particular matchup, since Taiga doesn't really try to "cheat" out of being hit. And, to top all of this off, Taiga has fought Saturn before, who seems to have a similar reactive power level shtick going on. Once she stops messing around and pays attention to that, it might get a smidge dicey.
That all said, there are four major things working in Zain's favor, here, I think
One: though he can't quite spam it at the beginning of the fight, as effectively, Teleportation is a pretty potent way to counter a glyph's Zone Control, and pulling it from his pocket a little ways into the fight to follow with an Isacoslash at least in theory might just end it then and there. Taiga's decently overconfident, it'd seem, and if she gets into a rhythm of just bullying him at range and repelling the odd Zero Wave she could get caught off-guard... except probably not, actually, Precognition's a pain to deal with. Even so, it's hard to lock someone down once they build the energy to get TP online with that.
Two: Zain has a very specific counter at this point for what otherwise would be Taiga's scariest hax.
Backing up to explain, briefly: Taiga has something called Black Ice, yeah? Basically cold-Amaterasu: "It is very hard to break and melt, and it can even turn fire attacks into ice for at least a week until it will start to break and become normal ice." Zain's primary favored element is fire, and he'll probably assume she's weak against it being an ice-element character, and that would backfire and get his stubborn ass beat in spectacular fashion except the Malkuth exists- "Mends and guards against Idea Fractures that correlate to the physical realm." Zain at this point can rectify the Idea Fracture present in how the ice doesn't function in the way that ice is supposed to, normally- he literally just did the same for the Banemist over Dragonwood, within his own canon. So, I suppose it would just behave like normal-ish ice against him, exempting the obvious Paralysis status effect (which he probably has at least one scroll for, at this point?) The Mind Over Matter power is very much an anti-Ailment power specifically for this, so Oof.
Three: Again, going back to Taiga's overconfidence, and how generally not effective zone control via Glyphs is likely to be for someone that can see/teleport around them, it's likely that this fight goes on a while... which means A: more time for Zain to build Kether/increase his stats, and B: as a consequence, a much higher chance of the Verethragna Form to come out. If it does, then just clicking the four second time-stop button, in combination with walking up and hitting Taiga over the head with a stick, probably kinda just wins. Taiga's defense without the power to react to the attack, while ">517" Tons of TNT, probably isn't going to going out so well against ">>3696" Tons of TNT. Worse yet for her, Summoning- definitely a good idea on paper- is almost definitely going to build up his Kether that much faster, whatever damage is pulled off not being worth it when compared to instantly getting gibbed by Nephesh.
...oh, yeah! Probably should go explain now: SBA requires that they be willing to kill, but otherwise in character. If it's not obvious that Taiga can do anything to him if she's unconscious/restrained, he's absolutely going for the nonlethal win with Peace Walker (which also applies Attack Down, to help him tank some of the hits he's probably taking as a result of this), and just tying her up for a month, since "stubborn in his refusal to not take lives needlessly", etc. SBA implying that the fighters somehow know what the win conditions of the match are, and that they're compelled to "win" before they can resume being in-character, has some funny consequences... in all likelihood, in this scenario, he'd just try to convince Taiga to give up (except he can't talk, so that probably just involves holding up sheets of paper or something), and even if she didn't would probably still refuse to kill if not necessary.
Character weakness: stubborn as all hell.
Four: On the other end of things, if Taiga manages to take him down and/or kill him, how does she deal with Regenerationn?
Even this early on, Zain's soul, mind, self, etc. are all able to last over a solid two minutes in the Banefall, which is generally potent enough to wipe away even an ordinary Archetype Armiger wielder's resistances to such within like, five seconds, let alone a normal person. It's not obvious from what I can see that Taiga can just eat his soul, so...
While the exact timeframe it takes Zain to return to life isn't entirely consistent or established, it's generally between an hour and a day. Definitely not over a month (which would constitute a loss under SBA), since that would contradict the several canon deaths he suffered plus the fact that Hero's Path only takes place over the course of a single year, about. Probably what would end up happening is Zain just blips out, for a while, and Taiga "wins" as far as she seems to be able to tell: Zain respawns in Colorado (the last point he'd attuned himself, at this point in the story) and just flies back to Nevada. If she's asleep when he shows back up and precog doesn't wake her up fast enough, it's just a thwack over the head, and she captured as above, or else killed if apparently unreasonable- if not, then it's a rematch as before, and all Zain has to do to win that if given prior knowledge is wise up, stay on the defensive for a wee bit, and activate the time stop to win. ...having a durability disparity and no time stop resist really is a hassle to deal with, huh.
This is more or less how his initial fight against Tessera went, come to think of it...
So, yeah, a TLDR of what I can see for the Win Conditions-
Taiga: Permanently paralyze with Black Ice, which probably requires re-application, and/or something else creative that might deal with the guy. Maybe (very unlikely, I think) Soul-steal would do the trick.
Zain: Basically a single hit or three past her defenses ought to do it, and if that can't be accomplished between the spells, stat amps to pierce ice barriers, the odd scroll or two to cover his mistakes, etc., there's always the ol' Verethragna into Nephesh combo.
Given Taiga's lack of knowledge on how the Tiphareth Shell works, I'm pretty sure she won't assume he'll revive, which means he definitely gets at least two tries if not more- I'm less sure Taiga has a way of getting out of being restrained by someone with Class 25 Strength given her apparent lack of any sustained/lifting strength feats... much less, a way of getting out of being stabbed, if that's what it comes down to.
So, yeah, that's about the size of my argument. Taiga have anything up her sleeve I'm missing, @Spinoirr?