Finally found the skill that Taiga has and it's rather appropriate. Unshaken Will: Protects user from Rage/Confusion/Fear/Silence/Enervation.
Taiga has an Asura persona then?
That's correct. Unshaken Will is a skill unique (i.e. non-transferable) to Asura, the ultimate persona of the Sun Arcana. Other than being too OP (level 86) and kinda far from the Shintoism-based thematic of the rest of the I.T.'s personas, it could be a good match for Taiga.
Looking at the
wiki page, I particularly like the fact that different cultures think of asuras differently. They're protector gods in Japanese Buddhism, but others see them as "jealous gods addicted to various malign passions". Nevertheless, asuras are always kicking ass and butting heads with someone (usually devas), which is something I can respect.
Personally, I would like Taiga's initial persona to be tiger-based. Taking something you hate about yourself and turning into your own strength is just too fitting for a Persona 4 fic to pass up. For her Evolved Persona at Rank 10 though...
*puts on geek hat*
Back to Taiga's resistance to hypnosis, there could be other explanations like a natural resistance to thaumaturgy in general, especially as pissed off as she was at the time. IIRC, she managed to resist Rider's Blood Fort Andromeda and keep herself conscious for a lot longer than a non-magi like her should be able to and only seems to get hypnotized in anime adaptations or
that Fate/Zero drama CD where Waver Velvet had to use hypnosis to make Taiga stop looking for certain oversided wine thief. Incidentally, Iskander playing interpreter between her and Waver was what later inspired her to ask Kiritsugu for English lessons.
If we assumed that Taiga's immunity to Kirei's spell was a Persona-related skill other than simply awakening hers, then
Resist Confuse (available to Berith, Principality and Queen Mab) or
Null Confuse (Power, Gorgon, Jatayu) are good candidates if we consider Confusion as the closest equivalent to Hypnosis within Persona 4's game mechanics. Alternatively, something like
Fast Heal (rank 3 skill available only by Skill Change in vanilla and to Kaguya-hime and Kanji's rank 4 bike skill in Golden) or
Insta-Heal (Norn, Helel) might be an option too, but these passive skills do their thing
after falling for the status effect, not before.
Finally, Taiga could be just that lucky. Or rather,
Lucky. A high Luck stat goes a long way to prevent the player from falling for a Status Effect or Instant Death skill. It also reminds me of that one (sorta) Shirou×Taiga doujinshi where she's his Servant during the war and shrugs off Gae Bolg because of her EX rank Luck Stat (really).