Author Notes: While the progression of the story roughly follows that of the show, many events are changed, arranged in a different order or omitted. This is fan fiction, after all.
"Are we packed up and ready to go?" Aang lifted his pack onto his shoulders.
"Yup, Appa's ready," Katara called out from above, "oh, so is Momo!" the lemur popped out from behind Katara.
"All ready to go," Sokka mounted the Sky Bison.
"Then we proceed as planned earlier," Mitsu levitated over Appa's head, throwing him an apple.
"Ready, Aang?" Toph cracked her knuckles.
"Ready when you are, Toph." The two elevated a platform of earth and raced towards the Wall. Appa followed slowly behind them, lest he be shot at by flying boulders. The people are the port were told security was tighter than usual at the Ba Sing Se terminals as well as at the Great Gate for some reason, though one look from the glowering Dai Li agents silenced any queries. One last ferry was allowed to dock at the city before the marine gates were shut, and it happened to be the one with Zuko, Iroh and the Freedom Fighters. Other ferries were temporarily halted and searched, which is why Sokka planned to avoid the ferry altogether and with Appa and Toph's help the group was to literally scale the Outer Wall and warn the Earth Kingdom soldiers about the approaching Fire Nation behemoth.
"It looks like a giant screw," Sokka looked through his telescope.
"That's no screw, it's a drill," Katara took her turn at the eyeglass. "It's too obvious what they're thinking."
Meanwhile, Toph and Aang were motoring their way to the wall's lower edge as Appa followed closely behind in the shadow of the wall as it lengthened towards them. The Earth Kingdom guards on the wall moved in rotational shifts, but their focus was on the Fire Nation force headed towards the northeastern gate on the other side of the city.
"We're here," Toph melded the rock with that of the wall, "going up!" She and Aang cycled their arms upwards, lifting the platform up. Appa hovered beside them, now totally shielded by the wall's enormous shadow. Explaining a giant Sky Bison would be strange enough, but this was the best way to get to the top. Their speed was accelerated by Mitsu pushing the platform upwards with his bending, and soon enough the Avatar and his friends were standing on top of the great Wall of Ba Sing Se.
They did not go unnoticed though, as a hundred or so Earth Kingdom soldiers were around them in a matter of seconds. Their leader was a hunchbacked general with a strange eye, who laughed at the Avatar's warnings of a giant drill.
"The city is impenetrable, that's why it's called Ba Sing Se, not Na Sing Se…" he crossed his pockmarked arms. "I've sent out a squad of elite Earthbenders to stop that thing, they're called the Terra Team," he invited them to look through the mounted scope.
Sure enough, a group of yellow-clad Earth warriors were already approaching the giant drill, flipping tanks over with ease and shunting rocks at the metal behemoth. The colors of War Minister Qing were on the mast of the metallic beast, but Aang and Katara had a sneaky feeling a certain Fire Nation Princess was on board as well.
"Bet you five pieces the circus freak and the Queen of the Glum Slum are going to come out soon," Sokka held the money out to Toph.
"That's a dumb bet, I've got nothing to bet against that," Toph shrugged, grinning.
Sure enough, Ty Lee and Mai popped up out of a side hatch, Mai's throwing knives raining down on the Earth soldiers. Those on the wall watched in awe as the circus trained girl disabled the entire team with precise strikes, leaving them paralyzed and unable to bend or even walk.
"The Terra Team is terrible," Sokka jibed, although his look was serious. "I have a plan, but we have to get those men out of there first!"
"Leave it to us to give you cover," one of the sentries lifted a rock and bent it towards the two girls. They retreated, but only as far as the hatch they came through. Knowing Mai's knives and Ty Lee's speed, the boulders were only going to crush the prone soldiers as the enormous drill carried on extending like an earthworm to the Outer Wall.
"Leave it to me," Mitsu put on the mask Aang saw him wear at the library.
"Why are you putting that on?" inquired the General.
"This is formal war, in the tradition of Avatar Kyoshi. Besides, I might want to go out with them someday," his grin was visible underneath the owl-like eye mask.
"Humph," Toph crossed her arms and looked away. Sokka raised an eyebrow but turned to Katara. "We're going to need some water for this plan, General."
"Take all you want, but what for…?" the general began to sound terrified at the ever louder sounds of the drill approaching.
Mitsu leapt off the wall, dodging the last hail of boulders from behind him and Force Bending them at the drill. The machine simply gobbled them up, but the way was clear for him to land beside the prone Terra Team, staff in hand. Two Earth Kingdom troops hurriedly bent a hole through the wall and began the extraction.
"Who's that?" Ty Lee prepared to grapple down with Mai. "I haven't seen him before."
"Who cares, it's another guy with another weapon."
Ty Lee leapt into the fray, but she found herself running into an invisible wall as Mitsu walked slowly towards her, pushing her back. Mai's knives just bounced off the invisible shield as the Earth troops quickly dragged the last of their stricken men through the hole, which they promptly sealed.
"Hey, no fair!" Ty Lee fell to the ground after an ill-advised flying kick.
"Who is this?" Mai picked up her deflected knives.
"I'd like to ask you to leave," Mitsu spoke in a deeper voice than usual. "Please?" he smiled at Ty Lee.
"Um…" she thought about it for a second, but Mai slapped her on the back of the head.
"No? But it's not fair, two fair skinned beauties out here in the boiling heat trying to bore through a wall?" Mitsu shrugged.
"He's got a point…ow!" Mai gave her best shut up look to Ty Lee.
In the corner of his eye Mitsu saw Sokka, Aang, Katara and Toph run to the other side of the drill, disappearing down an Earth bent hole and reappearing on the other end, near the slurry drain.
"Why don't you fight us hand to hand, or are you using some trick to hide your lack of skill?" Mai pointed to Mitsu. "And that mask… who the heck fights with a mask?"
"The Blue Spirit," Mitsu took a fighting stance.
"You've heard of the Blue Spirit?" Ty Lee looked at Mai. "The thief prince of the Fire Nation?"
"I've heard of him, you could say I was inspired."
"Let's see how inspired you are by this!" Ty Lee leapt into Mitsu's stance with a swinging roundhouse that only connected with his staff. The pain of hitting the titanium staff was immense as Ty Lee's toes instantly inflamed and filled with blood.
"That hurt!" she realigned herself, focusing on her unhurt foot.
"Using the Dead Hand," Mitsu twirled his staff to deflect Mai's knives, "an old technique once taught to non-Benders all over the world… impressive."
Ty Lee was getting frustrated as Mitsu blocked every tap and jab she tried to make on his pressure points with his annoying staff, which she could neither move nor touch offensively. Her knuckles were throbbing now, together with both her toes and one of her shoulders, thanks to a lone strike from the metal staff. Mai tried close combat, but found herself thrown into Ty Lee.
"Hey, there's another one!" Mai pointed to Toph, who was outside trying to hold the drill back with a massive rock outcrop. Mai threw a single knife at the Earthbender, but the blade stopped in midair and dropping dead onto the floor.
"Don't you touch her now," Mitsu approached Mai, though he swung his staff backwards and knocked Ty Lee out cold. He grabbed Mai by the collar and threw her below the rolling treads of the drill, where she sunk into a shallow hole courtesy of Toph. The treads would roll harmlessly over her, but she would not be out for a while thanks to the drill's slow speed. Dragging Ty Lee by her feet, Mitsu moved over to the struggling Earthbender.
"Hey, need a hand?" He yelled over the sound of heavy machinery.
"I'd like ten thousand! Hey, go inside and bend all the metal you like!"
"That's not how my bending works! There's too much metal here, plus it's riveted together tight!" Mitsu looked up. "Where are Aang and the others?"
"Inside, Sokka has this plan to hit all the pressure points on this thing, like the flea jumper here does! If you can't bend this thing, what are you going to do?"
Mitsu leapt into the open maintenance shaft, grasping a handle. "I'm going to give Sokka a little hand with his plan. Oh, find a hard hat, willya?"
"Very funny, wise guy!" she pushed even more rock upwards into the wheels and treads, which seemed to slowly gobble it up.
Mitsu's footsteps clattered on the metal behemoth as he ran towards the rear, passing by a frozen Fire Nation engineer whose backup plans he snatched out of his hip pouch.
"Thank you, Katara," he Force Bent the staff above his head as he balanced the unconscious Ty Lee on his left shoulder and the plans in his two hands. "This looks promising, a pipeline for extra rock and water…"
While Aang and Katara toiled at breaking the braces that held the drill together, Mitsu went the other way until he found a hatch labeled "Slurry". Just as well, since Ty Lee began to stir. Her eyes opened to the sight of a river of rock, mud and water flowing to a dim light in the distance.
"Hey, what the!" her hands were at her sides, crammed into the walls of the hatch.
"Time for a swim, princess," she felt his heavy boot knock her into the river of sludge, and then heard the hatch shut behind her. The current was extremely powerful and dragged her out of the way in no time.
"Right," Mitsu looked over the plans. He took a group of metal wrenches and with precision magnetized them to nearby nuts and bolts. By turning them all at the same time, the panels slid off easily, revealing the humming motors that drove the drill forward.
"Announcement, we have made it to the wall of Ba Sing Se!" Qing's voice cheered over the communication tubes.
"Oh no," Mitsu saw what drove the engine- about thirty Firebenders, led by a certain General with green flame whips.
"Well, if it isn't the kid from the desert slum!" Admiral Chan's hands glowed with his trademark green fire.
"I'm amazed you survived that Fire Bomb… especially since you left your men there to burn with it!" Mitsu made a fist while the Firebenders looked puzzled at their leader.
"Don't look at me like that! Keep the engine flames burning! We've reached the wall, and I want to be the first general over that wall! Finally, I will have equaled the Dragon of the West!"
"You're nothing like him," Mitsu leapt into the engine room and showered all the engineers and Firebenders with the wrenches and all the other tools in the room. Fire shields were no use against metal weapons, which knocked many out cold and others onto the floor.
"We'll see about that, boy!" Chan's feet thundered onto the control console, beside the unconscious engineer that was manning it. Chan's green flame washed over the spot Mitsu was standing, but he was not there. Instead a pipe narrowly missed his ducking head as the other Firebenders began to flee the engine room, where a multitude of uncontrolled fires were spreading. Some tried to control the fire with their bending, but gauges were exploding and chemicals were burning as well, making it a hopeless situation. Chan's blasting at the dodging Mitsu wasn't helping; the fire drill manual was burnt to a crisp, while the metallic plate with emergency details was melted by the green fire.
"Warning to all personnel, abandon drill! Abandon drill!" Qing's voice came over the loud tubes, "Slurry pipeline has been blocked by unknown object or force! We're going to break apart!"
"He's done it!" Mitsu raised a fist in salute to Aang and the others.
"Done what?" Chan saw that he was the last Fire Nation person left in the crumbling room.
"Made sure you can settle for Weasel of the West," Mitsu force bent the admiral into the metallic wall and turned to leave the corridor. Aang had hit a prime point in the front of the drill, which made all the braces he and Katara cut slide off. The engine room would have held the drill together, but it too was collapsing. Mitsu had to duck flying shrapnel and falling bolts as he fled, but the slurry pipe was now blocked by a fallen girder. The only way out was up onto the roof, so he bent the fragmented roof metal apart, landing on top of the drill. He could make out Aang on the far side, covered in earth and mud, with Momo licking it off of his master. He waved to his friend, but barely dodged the flame sucker punch that was behind him.
"Must I bow in front of her Royal Highness?" Mitsu used the same deeper voice as earlier.
"Get out of my way, stranger!" Azula was already generating lightning, her eyes brimming with hate for Aang and all his friends.
"I think you have to find your way first," Mitsu force bent the floor under Azula, whose off balance lightning shot harmlessly into the air. "You're not lost, just walking backwards from the right path. Besides, you're kinda cute."
"Damn you all!" Azula cursed as she fell backwards into the slurry pit, where a disheveled Ty Lee was slumped.
"He called you cute?" the acrobat got was a slinging of mud in her face. Mai could be seen sliding out from under the stalled tread, brushing off the dirt on her clothes.
"We lost," her deadpan look not helping the situation. She had a hint of a smirk, as she was relatively clean compared to her two friends. More Earthbender soldiers had come down the wall now and were finishing the drill off while Fire Nation airships were, instead of raiding the city in glory were picking up fleeing troops who fell over each other to grab the lines. Five men lifted the General and the Minister onto a larger balloon, the former still wrapped in metal paneling and the latter fretting about nervously.
"Retreat!" the Minister barked with a bullhorn as some of the airships were pelted with giant flying boulders.
"Retreat ?" Azula grabbed the captain of her balloon by the collar, "The Avatar is down there!"
"Forgive me, my liege! If we stay here we'll be crushed… literally!"
All Azula could do was kneel on the balloon's platform and scream