Avatar in my head and I was thinking about Maiko and Mai.
Now, Mai's character arc in Avatar, from my interpretation, is rediscovering herself and her wants and personhood that has been stripped from her as a noblewoman part of a family that submitted to the Fire Nation Imperialist structure and Ozai. We see in Book 2 set up for this. Mai in early Book 2 does not resist Azula's will aside from brief sparks of rebellion where she isn't present. "Of course not, Princess Azula" she notes formally and apathetically when Azula asks if she "minds", knowing she has no choice as Azula 'just' ponders if Mai's hostage brother is worth an Earth King like Bumi. Mai is always aware that Azula, as Princess in an authoritarian nation where the Fire Lord is God, can have her executed and her family punished. The unequal power dynamic is surprisingly consistent in the show.
Mai can't even insult Azula back in Zuko Alone as a child. She just lets Azula put an apple on her head (as Ty Lee loyally sniggers along), set it on fire, and when Zuko pushes her into the fountain to put it out, Mai, drenched, glares and says "You two are such… ugh". We know Mai can have an acid tongue, yet her fear of Azula prevents her from using it. Her most rebellious act in Book 2 is when she says "She can shoot all the lightning she wants at me. I am not getting in that wall sludge juice". Mai actually has self-respect, but she can't express it in the presence of greater threats, meanwhile Ty Lee merely says "Come on! Azula said we have to follow them", because Ty Lee follows Azula's will even when she isn't there.
Even when Mai gets with Zuko, she falls into a subservient role. When Azula interrupts Maiko's smooching, lazily dismissing Mai with "Oh Mai, Ty Lee needs help untangling her braid" Mai responds quickly "Sounds pretty serious" with only a touch of dryness and leaves, only able to muster throwing Azula a dirty look a split second after passing her. However, this little ember of rebellion will grow.
Mai has continued difficulty understanding Zuko's anger and reactiveness, or how to even function in a relationship. She initially tries to joke in a dismissive fashion, as if saying 'ugh, feelings are lame, right?', but that would only work with Azula logically. The Beach episode is a key Mai episode. She continues to be emotionally repressed, to the point Zuko, Ty Lee and Azula comment on it. However, Zuko's insecurity at her talking to Ruon-Jian to the point he physically removes him from her presence, and his accusative comments like "You like him, don't you?", also makes Mai feel a little boxed in, controlled, and that does irritated her given her history. However, at the Beach's emotional narrative climax, Mai is able to finally express herself at the rest of the group (Azula included) for the first time, telling them to "Leave her alone" and that she's "still mad". After Zuko explosively reveals the extent of his pain and confusion, we see a 'smoothing' effect on her attitude. She realises her and Zuko are dealing with pain in different ways and his way is understandable.
Mai says softly, "I know one thing I care about, I care about you". This is the one thing Mai can grasp in the confusion. This is where Mai betraying Azula becomes inevitable. We see Mai continue to be more supportive with Zuko, more actively trying to cheer him up in Nightmares and Daydreams with big smiles and jokes while Zuko remains shut down over the War meeting and is acting irritated and repressed due to his family trauma. When Zuko later leaves and joins the Avatar, Mai is hurt and angry, which shows in the Boiling Rock, saying "All I get is a letter? You could have at least looked me in the eye when you ripped out my heart". They have a tense conversation, but it's their most honest one. I actually think Mai already made up her mind in this scene to support Zuko over Azula, and she doesn't quite realise it. "Save it? You're betraying your country" she accuses, to which Zuko replies, resolute, "That's not how I see it", and in response Mai just folds her arms and turns her head away in an almost defeat.
I find it very telling she doesn't respond. It's because she realises Zuko is more passionate and resolute about his mission than she is hers. It's because she knows the Fire Nation under its current authority is not exactly great. Sometimes in life we fall into a box and we need someone to give us that little push so we can realise we can climb out of it, that the toxic space we're in isn't normal, and we don't have to tolerate it. I like to think Mai was thinking in that moment where Zuko locked her in the cell and he and she gazed into each others' eyes, what she was really thinking about was what life she actually wanted to live. She was thinking of Azula and being under her thumb, and she was thinking of all those moments with Zuko, like when they were lounging on the sofa together, smiling and joking in Nightmares & Daydreams, and she realised how ridiculous it was to be afraid of Azula killing her when the real fear should be being Azula's servant until her dying days, decades of repression and misery.
After all, what does Mai have left to fight for? Fear of Azula? Hah, what a joke. She remembers "I know one thing I care about. I care about you" and when she sees Zuko about to die she has to intervene.
"I guess you just don't know people as well as you think you do. You miscalculated. I love Zuko more than I fear you" Mai says to an increasingly-enraged Azula's speak of 'consequences', because Mai did fear Azula, but now in her love for Zuko she has found a purpose she has been lacking, her feelings and wants over Azula's will. Zuko being true to himself is contagious. Iroh's love for Zuko puts him on the right path, and in turn the love Mai has for Zuko saves her. As a consequence Ty Lee chooses Mai and their friendship over Azula's toxic, fear-based one and even later bonds with former enemies like the Kyoshi Warriors. Like Zuko says to Ozai, "an era of peace and kindness" will replace an "era of fear". In the face of fear, love and empathy win.