This is a "Dabi is a Todoroki" moment all over again. It's like, it's kind of obvious that Hagakure is the UA traitor, yet you fully believe that's the case due to how obvious it seems. However, we still don't know what to think about the circumstances behind her role as a traitor. My theories so far are:
- She had a rough childhood due to her quirk, and she just wanted to be seen, to be useful to someone, and when she was at her lowest, AFO came to solve her problems in exchange of something.
- She's a high-end nomu. Like even better than Kurogiri, Garaki has achieved making a nomu capable of passing as a normal person.
- She was abducted at some point, or maybe since she was a kid, and has implanted in her a dormant quirk, kind of like the one Lady Nagant had before exploding, and AFO can activate it remotely. Maybe it's a brain-washing type of quirk that lets him control here remotely, maybe he used an hypnosis quirk that has an specific trigger or maybe it's kind of a possession quirk or something that lets him see through her eyes and influence her actions.
- Maybe it's just Toga. Toga hasn't make an appearance, and with her awakening, she can keep tooru's quirk active (really, tooru's quirk is invisibility, we don't know if Toga's quirk before the awakening would transform into what Hagakure would look like if she weren't invisible, or if she would have been invisible too).
These are my best guesses, so even if Hagakure is the traitor, I would like for the reveal to go beyond of "Yeah, I work for AFO, he was giving the chance to live a normal life"