The past four days had been high up on Zuko's list of worst days of his life. He had been very lucky that his mother and his uncle were there to keep ruling the palace, because he had been absolutely useless. He was paranoid, stressed, and his temper was getting the better of him every time, to the point he decided to stay in his chambers and not come out until it was time to leave and prepare for the fight against the rebels. Ursa and Iroh had been very understanding, but were also concerned, both for him and for themselves - they had been very tense since Zuko full on threatened to cut them out of his life if didn't support his marriage to Azula.
If things were different, maybe he would have felt guilty. But at the moment, all he could do was obsess over every little thing that could possibly (and impossibly) go wrong with this plan.
Sokka had tried talking to him, told him about Aang's freak out before the eclipse and offered his help. Iroh told him stories about the fear he and other men felt when important battles were upon them. Chise and Mayu had listened to him, given him advice, and even went as far as too give him some of the meds they sometimes gave Azula when she had gone too many nights without sleeping at all. But nothing had helped, and by that point he knew very well that nothing would. He wouldn't have even a second of peace until he saw his sister again, which was scaring everyone around him.
Still, somehow, when it was time to prepare for the fight, he had found a way to get it together. Not only was Azula counting on him, he also had to defend his nation and do everything in his power to not let the efforts of everyone that was supporting him at that moment go to waste. It was his duty to do this right, and that was what he was going to do.
So he prepared to leave and was the first to be ready to go. When he and his allies made it to the fort where they would come back to after the battle, Zuko immediately started making sure everything was as it should be, going over the plan again, checking if everyone was fully prepared and if there was any kind of problem with any of the armors and weapons they would use. He paid special attention to the Yuyan archers - and to the poison they would use on their arrows. It likely wasn't enough to kill a person, but it did lead to almost instant sickness, which would leave their enemies disoriented and weakened. Some people had such strong reactions to the poison that it prevented them from bending. He just knew Sokka would never shut up about being able to find something like that, and even though he was already annoyed, Zuko had to admit that it was more than fair
Despite her not being there, Zuko also took his sister into consideration. She had sworn she had agreed to let the Kyoshi Warriors escort her to safety, but Zuko knew her better than that. He had not believed for a second that Azula had truly agreed to stay away from battle, and he had already told Suki, Ty Lee and the two Dai Li agents under his command to restrain his sister and make her leave the battlefield. He had also made it very clear that they would have to be extra careful with her, and that he wouldn't accept if she so much as got a simple scratch on her while being taken to the fort where he would meet her later. It didn't matter that she claimed to be fine, something had happened to make her feel unsafe staying among the rebels for long, and he wasn't taking any chances.
He had been freaking out trying to guess what it was that happened. Had she lost her bending like he had when he joined the Avatar? Was she struggling to tell what was and was not real again? Was she pregnant? Was she sick? Had any of the rebels somehow made her fear for life? Was there something obvious he wasn't seeing? Some possibility he wasn't considering?
All those questions and worries only made Zuko feel even more guilty. Azula had forced him to let her act out that insane plan she created, but he was still kicking himself for not having stopped her. He should have chained her to the bed, locked the bedroom door and told every guard and warrior in the palace to not let her leave and to not let anyone so much as see her without his permission.
If anything happened to her, it would be his fault. Azula was literally recovering from a breakdown. He was supposed to be the sane one. He was the one who insisted, against everyone's wishes, to be the person solely responsible for her recovery and for keeping her out of harm's way. He should have known better.
And he did know better now. Once he brought her back home, he was never letting her out of his sight again. He would die before letting her get hurt.
But first he had a battle to win.