Days went by and Zuko felt both more at ease and more tense by the hour. Years of exile and months on the run made him wary, and possibly paranoid. But its only paranoia if they aren't out to get you.
The earth kingdom generals were in a better mood to cooperate after days in the dark and a visit from Azula. Ty Lee would render them immobile, Mai would play with her knives and Azula would read their nightmares and then make them worse. Even Ty Lee didn't utter a word or blink an eye against this; she knew of the Darkest Day too, and knew what was at stake. They had to know as much as possible, and these generals were the very ones planning the invasion. The ones trying to make another Darkest Day.
Now they knew where the Avatar had discovered dark-days. And as troubling as a spirit library was, it seemed this Wan Shi Tong wouldn't be letting anyone else steal from him. A shame Zhao didn't do a more thorough job of destroying information about their nation. Though at least he had tried. Who knew what else might have been discovered?
The main danger had already been averted; Ba Sing Se would not be sending troops. If enough earthbenders got into the capital while they were stripped of their firebending, they could dig in and drag out the fight. There was still a risk of this if they managed to rally enough of the south, though.
And if they flew north... Even the northern water tribe would send men once they knew of the dark-day. It could not be allowed.
What he wouldn't give for a flying bison of his own! To be able to soar effortlessly over land and sea in days instead of weeks... Sozin was a fool for establishing and encouraging dragon hunting.
Dragons had allowed some master firebenders to reach the Air Temples for the first strike, and to hunt those on sky bisons down. Sure, most dragons had been wild and to kill one increased firebending power. But tame dragons were even more useful than merely more powerful soldiers. Surely a balance could have been found, with only the most wild dragons being slain for power. But now they were all dead.
And uncle Iroh, Dragon of the West, had slain the last one.
...Which now that he thought about it, was highly unlikely. Make it tea and tell it cryptic tales, sure. But slay it? One of the original firebender? After he had just broken down from the loss of his son? No way.
It was something to think about.
In the meantime patrols would be increased at the north and, well, everywhere, and scouts spies would be sent further into earth kingdom territory for advanced warning. And so there was nothing left to do but wait for backup and train. At least the training was interesting.
He could create lightning with almost as much skill as Azula now, if less speed and precision. But each day let him separate the energies with greater speed and each blast let loose let him work on his aim. Azula had perfected redirection on the second day and had redirected his lightning flawlessly several times. But he took so long to charge each blast, and they were still weaker than hers, so she came up with a better plan.
Thus began the most dangerous game of catch the world had ever seen. She would cast her lightning at him, he would redirect it at her, she would send it back, and they would repeat until one grew tired and aimed it elsewhere. Given how exhilarating and energising it was, this took quite some time.
They soon realised that they could draw the lightning towards themselves if it was close enough; it seemed to want to strike them, arcing towards their waiting fingertips even when aimed poorly. They began alternating between practicing accurately hitting each other and testing how far they could pull it towards themselves.
Eventually they realised how useful this could be. One of them on either side of the enemy, they could send the same blast back and forth between them rapidly until all enemies were down, or they hit a particularly agile target.
Lightning was soon aimed skyward, too.
Oh, this was going to be fun.