Disclaimer: How many times must I say it? I don't own Zim.
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Several days later………
Zim was exhausted. Zak's training was harsh and unrelenting. Even though Irkens did not need sleep, Zim at least wished he could take a break to relax a bit. And to make things worse, Dib seemed to be getting more aggressive lately.
A few days after Zak had arrived, Dib finally decided to take action on his suspicions of Zak. He snuck out of lunch early, stole a bucket from the janitor, and filled it with water. He then returned to Ms. Bitters' classroom. Fortunately for him, the evil teacher was not there. Dib quietly went to the back of the room and poured the bucket of water all over Zak's chair. "Now, if this water burns Zak, then he really is an alien." Dib said. "Am I still talking to myself? Why do I keep doing that?" He then hid the bucket and went back to lunch. Gaz did ask him where he'd been, but the bell rang before he could stammer a reply.
Upon returning to Ms. Bitters' class, Dib immediately turned in his seat to watch Zak. As expected, Zak was burned by the water upon sitting in his seat. He jumped up and ran back and forth, yelping in pain while clutching his ass. Zak seemed to calm down much faster than Zim, however, and swapped his seat with a spare one off to the side before sitting down again. As usual, Dib was the only one who saw Zak's pain, but that was all he needed. Zim, meanwhile, saw Dib watching Zak and grinning and drew the appropriate conclusion.
After skool, while Zak and Zim were walking to Zim's base, Zak asked about the incident in the classroom. "I sat in something wet and suddenly felt like my ass was on fire."
Zim snarled. "It was the Dib. There can be no other explanation. And the wet stuff was water. I'm not exactly sure how or why, but liquid water burns us. Once we get back to the lab I'll show you how to protect yourself from it."
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Once back at the lab, Zim made good on his promise and got Zak a paste shielding. Once that was done, Zim told Zak that "now Dib knows you're an Irken too. He'll try everything he can think of to expose us, so GET OFF OF ME!" The last part was spoken not to Zak, but to Gir who had decided to climb up onto Zim's back. Gir jumped down and stood by Zim's side, staring at Zak.
"WHO IS THAT!" Gir shouted, pointing at Zak and turning to look at Zim.
"That is-"
"WHO IS IT?"
"That is-"
"WHO IS IT?"
Zim waited for Gir to stop shouting, then spoke through gritted teeth. "That is Zak. The Tallest sent him."
"Oooooooooh" Gir said quietly. "I'm gonna go play with Pig, 'kay?"
Zim slapped his hand to his forehead and sighed. "Okay, Gir, you do that."
As Gir walked off, Zak looked at Zim. "What was that?"
"That was Gir, my, eh, SIR unit, sort of. The Tallest told me he was advanced, but now I'm not so sure…"
"Riiight," Zak said dismissively. "Anyway, back to your training. You are making progress, but very slowly. Although I do have an idea that may help you learn faster. You have already heard all the lessons I am trying to teach you, so let's see if a duel will get it into your head."
"A duel?" Zim asked, confused.
"Yes," said Zak. "We shall do battle, one-on-one. Hopefully this will drill the lessons into your head."
"Fine." Zim said, then led Zak to the hologram chamber. "We can battle here."
Zak nodded, then rose up on his spider legs and took a battle stance. Zim also rose up on his spider legs. Zim made the first move, charging Zak, who knocked him back with one of his legs. Zak struck next, knocking Zim to the ground. Zak then started stabbing at Zim with his spider legs. Zim managed to dodge out of the way, but Zak didn't give Zim any chance to counter-attack. The battle went on like this for over an hour. Gir entered at about the halfway point, slurping his Suckmonkey, but even he knew better than to interfere. So, he sat down on the ground and watched. Actually, he didn't "watch" so much as slurp his Suckmonkey noisily, but he did glance up every once in a while before returning to his drink.
As he dodged Zak's attacks, the realization finally hit Zim. All the things he'd done in the past were not things to be proud of. In that moment of clarity, of realization, Zim began to feel regret for the first time in his entire life. Now that he realized this, he could fight back against Zak's relentless attacks. He ejected a laser pistol from his PAK and caught it in his right hand. He then rolled directly under Zak to the opposite side of the chamber. Zak turned to see him, then used his spider legs to leap across the chamber at Zim. Zim aimed the pistol and fired. The blast struck Zak right in the chest, knocking him out of the air. Zak fell to the ground and looked at Zim, still clutching the pistol. Zak stood up and slowly began to clap.
"Excellent, Zim," he said. "You actually managed to land a hit on me. That is something no one has ever been able to do before. Congratulations. Did this battle teach you what I've been trying to show you?"
Zim looked at Zak, then spoke only one word: "Yes."
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A/N: Just so you know, Zim wasn't affected in any major way at all by this. Only thing is, he's no longer incompetent.