I rewatched Zuko and Azula's Agni Kai recently and it's left me wondering – when Zuko begins to goad Azula into striking him with lightning, was he making the decision to kill her?
Because had Azula shot lightning directly at him like he planned and not at Katara, the most forthright implication to me is that he was intending to strike Azula with her own lightning. And Azula, for all her mastery, would not have been able to counter that.
On the other hand, maybe he wasn't planning to kill her at all and was simply planning to redirect it elsewhere (similar to what he did with Ozai). But given the tone of tragedy throughout the Agni Kai, the fact that they both acknowledge that this fight will be "the end" to them, I don't think it's inaccurate to read Zuko's actions as him preparing to kill Azula, even though an Agni Kai doesn't have to end with death (and in canon it didn't). Also, why goad her into striking him with lightning if he wasn't planning on doing something intentional with it? If anything, it adds another layer to the tragedy to me, because I don't believe Zuko wants to kill her. And it stands in such contrast to the way that Azula desperately wants to kill him.
I also think that there would have even been something sadly poetic in that sort of demise for Azula should the Agni Kai had gone this direction: Azula, struck down by her preferred sub-skill. Azula, struck down by the very bolt of lightning that she intended to kill her brother with. Azula, struck down by her own power.
I think Zuko's position has always been that he'd prefer not to kill, but he's prepared to if he needs to defend himself or others. I do think he intended to do what he did to Ozai and quickly end the fight by knocking Azula to her feet, but I think he also knew that Azula was not going to stop and that he might need to kill her, which is where the sense of finality / tragedy is. Because Azula is definitely prepared to kill. She's the one who says that this is the end. Zuko doesn't say that, but he does call her bluff when she says she's "sorry it has to end this way," and I think that is him acknowledging that she won't stop until he and Katara are dead and resolving himself to the idea that he might have to use lethal force.
It's a direct call and reversal to what he said in book 2, when he backtracked on saying he needed to defend himself from Azula by saying she is his sister and he needs to learn to get along with her. He's now realized that it isn't him who is the problem, it's her, and she won't stop until he is dead, so defending himself against her isn't wrong, even if it means she needs to die. I don't think he wants that to happen, but he's not going to go out of his way to protect someone who is a danger to him and the people around him.
And I think that also fits with his stance in The Southern Raiders. He doesn't encourage Katara to kill, but he's against Aang trying to tell her it would be morally wrong, for the same reasons. He tells Ozai he won't kill him because he doesn't need to, but Ozai is correct in observing that Zuko came to that confrontation armed and ready to use lethal force if he had to.
And that's not inconsistent with Zuko trying to save Zhao, either. Zuko offers Zhao his hand, but he doesn't try to sacrifice himself to save Zhao, either. Zuko is clearly shaken by what happens to Zhao, but I think it's part of what he learns by the end of the series and his confrontation with Azula, that he doesn't need to put himself in harm's way for people who don't want to be saved, especially if those people want him dead.
Once Azula and Ozai are subdued, Zuko isn't interested in pursuing their deaths, nor does he say anything when Katara chooses to spare Yon Rah. He does tell Ozai that he's lucky the Avatar spared him, which does imply that Zuko would have killed him, but Zuko doesn't say that he wants to kill him now that he's imprisoned, either. And what Zuko wanted Aang to do about Ozai was always framed in Zuko fearing that if Aang didn't kill Ozai, he would kill him first. Once Ozai isn't a threat, I don't think Zuko particularly cares whether Ozai lives or dies, and I think that was the point of what he said, not that Zuko would have killed him if weren't for Aang, but that if it had been up to Zuko to stop Ozai, he wouldn't have any moral hangups about using lethal force if necessary.
