A Promise to Keep Part 1: Prologue

Summary: It began with a promise - an agreement made between two rivals that no matter what happened, and no matter who won, this single vow would never be broken. How far will they go to honor it? ZaDr.

Pairings: Zim x Dib

Setting: Post series, 10 years (2 years in prologue)

Genre: Drama, Action, Romance

Rating: Mature (Swearing, Violence, Sexuality, Xenophilia)

Beta Readers: Vertorm

Author's Note: This fic takes the cancelled episodes into account, especially Mopiness of Doom, 10 Minutes to Doom and The Trial. If you aren't familiar with them, then I'd be more than happy to lead you in the right direction. Also, this is your one and only warning that this story is NOT fluff. There will be many sad and upsetting moments throughout this fic. But, there will also be many uplifting ones too, and I can promise you that the ultimate ending of this story will be a happy one. Lastly, in regards to ages, two years passed in the show according to the Jhonen Vasquez wiki. Dib was 11 when the show began and 13 by the time it ended. Gaz was 10-12, and Zim 159-161 (15-16 Irk years, because also according to the wiki, 10 Earth years is 1 Irk year).

Disclaimer: I do not own Invader Zim, though I certainly thank the creators for their amazing work! Invader Zim is the property of Jhonen Vasquez and Nickelodeon, and is not my intellectual property in any way. There is no financial gain made from this, nor will any be sought. The entirety of this story is for entertainment purposes only.

Post series, 2 years - Dib is 15, Gaz 14 and Zim 163 (16 Irk years)

The sound of a giant robot crashing against the ground rang out into the night, destroying the once-peaceful bliss of sleep to those nearby. Energy pistol gunshots mingled with the furious padding of shoes against cement. But rather than rising from their beds, the nearby citizens merely buried their heads further into their pillows. It's not like this was anything new, and even if it were, they wouldn't have cared anyway.

There was a terrible sound of metal crunching and ripping. Dogs barked and cats ran from the scene as a car alarm began shrieking, the vehicle's frame quite thoroughly crushed under the weight of a large machine.

"Curse you, Dib!" Zim's verbal spat echoed between the buildings as he ran down the street, his Irken uniform wrinkling up against his skin as he escaped the wreckage of his once-giant robot. He had his gun pointed behind him, and his head was turned around just enough to see where he was aiming.

Dib recognized Zim's tactic immediately. With his wig having fallen off a ways back, the alien had his antennae pointed forward and on high alert. He was using them to warn himself of anything that he might be about to run into, so that he could keep focusing his eyes behind him at Dib.

Cheating alien.

"Curse me?!" Dib exclaimed as he shot at Zim from a couple yards back, the energy bolt just barely missing its target. The bottom of his trench coat flew along behind him as he ran, which he'd hastily thrown over his blue and white striped pajamas. "You're the one who attacked my house in the middle of the night!"

"Do you have any idea in that mushy brain of yours just how expensive that robot was?!" Zim barked and shot at Dib again. He would have hit him square in the chest had Dib not leapt to the side just in time.

"Don't care!" Dib hollered back, quickly closing the distance between them as he broke out into a sprint.

Zim hissed, his serpentine tongue flicking out of his mouth in irritation. Suddenly his left antenna twitched as he approached a tall building. He quickly pulled out his PAK legs and leapt into the air, pulling himself up and along the side of it.

Dib reached into one of the many hidden pockets of his trench coat and pulled out his Scaler Gun; a noticeably larger weapon than his energy pistol, though still able to be wielded with one hand. He pointed it up at the roof of the office building that Zim was climbing, and pulled the trigger. A cord shot out and attached itself firmly to the top of the wall, near the roof. With another push of a button, he was sailing upward.

Zim leapt from side to side with his PAK legs as Dib began shooting his energy gun up at him, each blast blowing off large chunks of the building and causing debris to fall to the ground below. Dib made sure not to shoot if Zim was directly above him for that very reason, but unfortunately for him, Zim seemed to realize why. He stayed just above him until he was able to leap onto the roof and out of sight.

Dib prepared himself. Zim would be ready for his approach over the top, but he had another plan! He quickly pushed a button on the Scaler, and the cord stopped retracting. His body hung down against the side of the building, just below the roof's edge. He waited a moment before pointing his energy gun over at the large McMeaties billboard nearby, and then shot at it a few times.

If his scheme worked, then Zim's attention would be over there now, and he could pull himself onto the roof without being shot at! So as quickly as he could, Dib hoisted himself up and over the edge with his arms. He rolled forward into a somersault and quickly pointed both of his guns forward once he was back up on his feet.

Zim was nowhere to be found.

Dib didn't even have a chance to tense up before something slammed against him from behind. It only took him a second to realize that it was Zim, who was now holding Dib's arms down against his sides. The alien's chest was pressed against his back, and his arms were wrapped around Dib's torso in a tight hold.

"Well, well..." Zim hissed with a dark mirth into his ear, causing a shiver to run down Dib's spine. Zim was the same height as him still, which only made him that much more intimidating. "Just as predictable as ever, I see."

Dib threw his head backward and smacked it into Zim's face, wincing immediately at the pain in the back of his skull. Zim gasped and his arms loosened just enough for Dib to pull free though, so it had been worth it! He shot the Scaler at a tree in the distance, and once it had connected, he pressed the retract button. Zim lunged just in time to grab onto Dib's waist, and the two of them were yanked forward.

Zim reached his PAK legs out as they flew toward the tree, clearly trying to stop their momentum by grabbing onto something. Dib wrenched and twisted in Zim's grasp, but he couldn't quite shake him off. He couldn't shoot at him either, Zim having managed to grab onto his other arm. After a few more seconds of struggling, they collided into the tree with a painful 'thud.'

Dib felt his Scaler slip out of his hand, and heard it clatter against the tree. His fingers slipped off the wood of the branches as he fell toward the ground, and his body slid painfully down their length. He could see Zim at the top of the tree, having grasped onto it with his PAK legs. Dib managed to grab onto a larger branch about halfway down though, finally stopping his fall and hanging in the air.

Dib looked up at Zim, who was climbing down toward him like a spider converging on its prey. His reflexes immediately kicked in - he yanked his energy gun up, found the red, malicious glint of Zim's eyes, and shot.

Zim gasped and he tried to leap away, but the energy bolt hit him square in the face. There was a shriek of pain as his PAK legs let go of the branches. Dib's eyes widened as Zim started falling straight toward him, and an ice cold realization of what he'd done filled his gut. He'd dropped his Scaler already, which left him with no way of escaping.

Tree branches snapped as their bodies collided. Metal PAK legs slammed against wood and dirt, and pained moans filled the space around them as they hit the ground together.

Dib blinked his eyes open and found the sky above them, having rolled away from the tree and out into a field. There was an empty playground nearby, and further off he could see his High Skool. Next to him was Zim, lying most ungracefully with his PAK legs all bent up or snapped off from the fall.

A few moments of silence passed, both of them winded and bruised, until...

"Dick," Dib's single word came out as more of a statement than an actual insult.

"Zim is no filthy reproductive organ!"

Dib looked over at Zim, and when he saw the dramatically serious expression on the alien's face, he burst out into laughter. His mirth soared out into the open space around them, and only a few moments later it was joined by another.

Zim's laugh wasn't evil; it held no malice or hidden intentions. It was genuine, and it was a sound that Dib had not heard too many times before.

Time passed, the two of them giggling and laughing at their ridiculous situation. It was probably more Dib's fault with the way he'd gone and blasted Zim in the face while he was hanging precariously above him. But then again, Zim had been the one to attack his house with a giant robot in the middle of the night. What a jerk! Not that it had been difficult for Dib to ruin it - Zim's plots never were. But lately Dib had noticed a big difference in the alien's plans compared to when he'd first landed.

It used to be that Zim would attack the Earth and Dib would come running to the rescue, guns and bravado blazing. Now days though, Zim took the fight straight to him. His plans would often include some sort of mass-Earth-destruction scheme as well, but he always picked the fight with Dib directly.

Dib had never been popular at any point in his life, not even when he was very young. His interests and opinions always wound up being what others considered 'un-cool.' Somehow, through some means or another, it always was that way. But that never stopped him! Perhaps it was because he had his father's stubbornness. He didn't care what anyone thought of him, even if it meant he'd never have any friends. The only thing he cared about was proving that the paranormal things he'd seen were real, and that he wasn't crazy.

Someday... Someday, he'd show them all!

But like anything that stands tall against a storm, there would eventually be chips and cracks in the exterior. The armor would start to rust, the tree would start to bend, and the small boy who had been picked on his entire life would finally give in to the desires of others.

And Dib did.

He'd announced his resignation as Zim's nemesis to the alien first, having decided to give up on studying the paranormal and defending the Earth. Of course Zim had cackled maniacally in response, but Dib knew it was what he needed to do. If Zim won because of it, then at least he'd die having finally been someone. His father would respect him as an accomplished scientist, he'd have friends, and no more would he be beaten up by a psychotic alien just because he tried to protect the very assholes that had made his life miserable for years. He didn't care what happened to them anymore, he hated them, and he was going to become something better!

His father had been proud, and for the first time in Dib's entire life, he'd seen him almost every day. They'd worked together on many fantastic science projects and discoveries, and Dib had even been in the news a few times! It was everything he'd ever wanted.

And yet, this time around, the wall crumbled to the ground, the armor rusted all the way through, and the trees fell over completely. Dib was faced with a harsher storm, one that left him feeling worse than ever before.

Being picked on, beaten up, losing to Zim, fighting for people he didn't care about, being told he was crazy because he really did see Big Foot... Those problems were nothing in comparison to the sheer loneliness he felt while working with his father. The empty hole that had been ripped through his heart was more painful than any bully or invalidation had ever been, because he'd failed his purpose.

His basic principle in life, to defend the Earth from evil no matter the cost, and to prove that the paranormal things he'd seen with his own eyes were real... That was who he was. It was a hard path to walk, and Dib had found himself beaten and bruised by it far more times than he could count. But it was the path that was true to him, and he'd wandered away from it, down into an empty, barren wasteland instead.

Dib had raced to Zim's house as quickly as he could. He probably should have realized that something was up from the fact that the gnomes didn't attack him, but he'd been too focused on other things. What terrible schemes had his enemy created without him around to put a stop to them?! As it turned out... there were none.

He'd found Zim sitting on his couch, staring mindlessly at the TV with magazines strewn all over the floor, and his house in complete, disgusting disarray. Even more shocking had been the fact that all of those magazines, and even the TV reports, were about him - Dib Membrane and his father, two scientists and their achievements. It seemed that Zim had also been left purposeless and empty from their change of pace, and the evidence was plain to see.

Dib did the only thing that he could, and loudly proclaimed himself as Zim's nemesis once again. Zim's eyes, once empty and glazed over, were immediately filled with life. And just like that, everything had gone back to normal...

Except for one very important thing.

Never again had Dib seen the same hatred in Zim's eyes that had been present before. Even in the middle of some of their worst fights, his expression was that of competition and excitement. And if he was being completely honest with himself, it was the same for Dib. The thrill of the fight, the love of the game... It was the result of realizing that neither of them had too much else going for them on their tiny spitball of a planet. Without each other, there was nothing to look forward to. There was no one to test their skills against, and there was no challenge.

It was that very line of thinking that caused Dib to ask a question that would change their lives forever.

"Hey, Zim?" Dib's voice was quiet now that they'd finally finished laughing, both of them looking up at the starry night sky.

"Hmm?" Zim hummed in response, though he did not move to look at him.

"Are you really going to destroy the Earth?"

Zim frowned, which Dib caught from the corner of his eye. Zim seemed to think for a moment, a heavy silence falling between them. Eventually his expression softened though, and Dib knew that the alien understood what he'd truly been asking. More than wondering about the fate of the Earth, Dib had been inquiring about them. After everything that had happened, had their relationship really not changed at all? Were they still just enemies, even when they had come to realize that their lives would be meaningless without the other?

"My mission is the same, Dib," Zim's voice was low, emphasizing its seriousness. "I will not fail or give up; not even for you."

Dib felt his eyes soften in sadness. He'd fully expected that answer, though there was still a part of him that hurt to hear it. Maybe he'd hoped too much that somehow they could just stop fighting…

"Then will you make me a promise?" Dib asked after a bit. "From one rival to another?"

At the edge of Dib's vision, he saw Zim's lips curl up into a grin. Never before had one of them described their relationship as a rivalry. They had always been each other's nemesis or enemy. Rivals did not hate each other though, and neither, really, did they. Rivals competed and opposed each other, their purposes leaving them butting heads and unable to work together. But at the same time, they were equals.

That felt more accurate these days. Dib didn't hate Zim, and he knew that Zim didn't hate him, even with all their blustering. They could never be friends or allies though, because that meant letting go of the thing that meant the most to them; Zim would never give up on his mission, and Dib would never let him succeed at it. So that left them with their rivalry, and the bitter knowledge that in another life, under different circumstances, maybe things could have been different. Maybe they could have even been friends.

But this wasn't another life.

"What promise?" Zim asked, still looking upward.

"I don't want to live in a universe where the Earth is gone," Dib began, his eyes glazing over with emotions. "That means I failed… I never want to watch my own planet burn or be enslaved. So promise me that you won't call the Armada or destroy the Earth unless you've killed me first."

Zim was quiet. He hadn't moved his head, so Dib continued to stare at the sky, waiting patiently for his response. Maybe he was asking too much and Zim would refuse, but he had to ask anyway. He had to try. From one rival to another, maybe, just maybe, they could have this one agreement.

After a strangely comfortable silence, Zim finally spoke. "In return, will you promise not to let me be cut open alive?" Zim's voice was much more serious than Dib had ever heard it before. "If you ever deliver me to one of your nasty research groups, do you swear to only give them a corpse?"

Dib finally looked at Zim, and Zim looked back at him. After a moment, Dib smiled and nodded. He'd be willing to promise just about anything to have the reassurance of never seeing his home destroyed. He'd have to already be dead, and then it wouldn't matter anymore. Zim smiled as well, and they both looked back up at the stars together in silence.

It wasn't a full compromise, but it was a start. They'd made an agreement out of their strange respect for one another, and maybe one day there could even be more. But this was today. Tomorrow things would go back to normal, and they'd be fighting again. So they stayed there for hours, just the two of them and their promise.