A/N Hey, my dudes! I got this idea from the very end of the episode Enemy of my Enemy! I hope you enjoy! And if you're one of those lucky people who believe full-heartedly that leprechauns exist, thiiiiis story may challenge those beliefs and you probably should not read it ¯\_(ツ)_/¯ just saying!
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"Has anyone seen my action-kick unicorn-man...?" A ten-year-old Michelangelo asked, peering under the couch cushions in his attempt to find his lost action figure. Donatello was on the opposite side of the t.v pit, carefully combining a few of this and a few of that together before stringing a couple of faulty wires together to create -low and behold- a new power source for his laboratory!
He beamed at the string of lights with profound pride in his ability to create something so complex, and imagined exactly where he was going to place it in his lab. Then when a moan sounded from the other side of the common area, Donnie glanced up to find Mikey's face smushed against the couch. He was clearly upset about something, but knowing Mikey, it was probably nothing. But Donnie still asked;
"What's wrong, Mikey?"
"I can't find my action-kick unicorn-man! I've looked everywhere!" He emphasized the last word before drawing out a long and unhappy moan while he pillowed his head against his arms.
"What's got his knickers in a knot?" Raph suddenly asked from seemly out of nowhere, and Donatello had to switch his gaze towards the dojo to see where the voice had originated from. And then when he spotted his immediate brother, Donnie pointed at Mikey and said, "he lost one of his action figures."
"Probably lost it in his dirty room."
"I didn't!" Mikey whined, sitting up from his position to toss Raphael a devastated look, "I put my action-kick unicorn-man on my nightstand just last night, and when I went to go get it, like, just barely, it was gone! I looked everywhere! But, but it's nowhere!"
And when Donnie switched his gaze away from Mikey's pity party to look at Raph, he noticed something uncomfortable flicker in Raph's eyes, something Mikey entirely missed. That look meant Raphael did something he wasn't supposed to.
"Uh... have ya checked the ground? Maybe it fell off."
"Yes!"
"Did ya check behind yer nightstand?"
"Yes!"
"Under yer bed?"
"Yes! Yes! Yes! It's gone!"
And when it looked like Raph had run out of wiggle room, he suddenly said something that caught Donnie entirely off guard;
"Then it sounds like the leprechauns took it."
Mikey's face went from devastation to confusion before switching to shock; "leprechauns?"
"Yeah, they're these itty bitty creatures that roam around and steal yer things when you're not lookin'." Raph said as he came closer to the youngest with the utmost serious look he reserved for once in a blue moon occasions. And when the information fell on Mikey's ears, his mouth rounded in an 'o' before he moved closer to Raph and sat down in front of him like it was storytime.
"Have they ever taken your things before...?"
"Oh yes. Those suckers are gonna get it one day."
And even though Donnie really wanted to point out such magical creatures don't and won't ever exist, something struck him as genius and he slowly closed his mouth while he began to contemplate the brilliance of this idea. There were countless times he took one of Mikey's things to do experiments on, or took them apart to see how they worked, or needed a test subject, but it always ended up to be a huge disaster when -if- Mikey found out his things were gone, thus, making the situation a lot worse when the youngest threw a huge, ginormous scene. Of course, Donnie always had to find a way to pay his little brother back when either Leo or Master Splinter found out, but if Donnie could blame Mikey's things disappearing on account of leprechauns... then Mikey would accept this tall-tale, and Donnie would no longer have to pay his little brother back!
"We should set a trap for them! Then when we have one, we can force it to tell us where our stuff is!" Mikey chirped while a smile crossed over his freckled features and he stood up with excitement.
"I don't know, Mikey. Leprechauns are hard to catch." Donnie suddenly came to his immediate brother's rescue, and ignored the surprised look Raph tossed his way, "no one's actually seen them before."
"Maybe we can be the first ones!"
"But I have heard that if you try to capture them," the third oldest quickly continued to smash this oncoming idea Mikey had into the ground, "it'll make them angry and want to steal more of your things. That's why Raph and I haven't been trying to capture them. We don't want any more of or things to go missing."
"So... if I set out traps, they'll get even madder and steal more of my things?"
"That's right, lil' bro." Raph chined in, pointing a finger at the youngest, "they don't appreciate any traps of any kind. I actually tried once, but they stole my drumset."
"No!"
"Yes." Raph feigned hurt, and Donnie suppressed a moan. Raphael's excuse was becoming a little implausible, but at least it was Mikey, who, in a matter of speaking, was easy to fool. The youngest would believe anything if the story was spun just right.
And while Raph told the tale of his missing drumset, Mikey looked enthralled with the story before a thoughtful look settled over his features. Then once Raph had finished, Mikey hopped up, bolted to the kitchen before disappearing inside, leaving the two middle children to silently smirk at each other.
"Thanks for yer help back there."
"No problem."
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The past couple of years after Mikey made the phenomenal discovery of leprechauns, he would sometimes leave special gifts as peace offerings around the Lair which Donnie and Raph took turns taking when Mikey wasn't looking. They had to keep up their lie somehow, and it became somewhat of a game to find all the hidden treatures Mikey would leave around their underground home.
Also, during the past couple of years, both Donnie and Raph helped themselves to Mikey's things, and if said things got lost, misplaced, broken, or exploded -in Donnie's case-, they would tell the youngest it was probably the leprechauns -which Mikey full-heartedly, one hundred percent believed.
Sometimes he'd complain to Donnie about the stupid magical creatures that lurked in their home. Whenever he did that, Donnie would nod in an assumedly understanding way and comment about how much he hated the leprechauns too.
The worse part about their plan they didn't foresee is when Leonardo found out.
Donnie was in the common area fixing the furnace so they could have a warm winter that year when Mikey sagged into the t.v pit sulking and pouting and featuring something that was completely unhappy about his current situation. That's what Leo saw when he came out from the dojo to watch a new release of his favorite tv show.
"What's wrong, Mikey?"
"The stupid leprechauns stole one of the comic books master Splinter brought back for me. It's gone and now I can't finish the series!"
Donnie's gaze drifted away from the led error light on the furnace control board to see Leo staring dumbfoundedly at the youngest. And after a good second or two, Leo slowly asked, "leprechauns...?"
"Yes! They've been taking my stuff for years! And even though I make them food and create houses for them, and sometimes little bathtubs, they still won't stop taking my stuff!"
"Leprechauns...?"
"Yes, Leo! Keep up!"
"But, uh...-"
"Hey, Mikey, did you check to see if your comic book is in Raph's room? He might have borrowed it without asking." Donnie suddenly interrupted and Leo's blue eyes left Mikey's face to switch slowly to Donnie's, every ounce of confusion visible in his face.
"No..." Mikey said while he thought about Donnie's suggestion before he yelled, "Raph!" and picked himself off of the couch and hurled himself towards Raph's room to probably interrogate the second oldest.
"Why is he talking about leprechauns?"
"It's probably something stupid Raph told him," Donnie said with a one-shoulder shrug before turning back to the furnace control panel. Perhaps it was time to tell Raph they should stop stealing Mikey's things.
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Donnie did tell Raphael they needed to lower the amount they took Mikey's stuff. And they did, doing it less often and completely at random -well, at least Donnie did. And when they turned fifteen, the lie was still up and going with no intention of letting the truth slip. If they accidentally did, and Mikey found out there was no such thing as leprechauns -and put two and two together to figure out it was them the whole time-, the youngest would probably blow a gasket or something. Both Raph and Donnie were not eager to see a truly angry Mikey when the youngest found out the truth. So after a secret meeting, they vowed to never ever tell Mikey and hoped the youngest forgot about this whole thing.
But again, they didn't count on Leonardo.
They should have told the oldest, should have confessed everything, but they failed to do so. And when they lost the mission to get Karai on their side, and Leo walked to the parapet sulking, Donnie didn't realize that Raph's and his secret would come into the light.
Donnie tried to help Leo feel better, but it flopped miserably. Then Mikey walked up to the oldest before sighing;
"I've been there dude, for me, it was leprechauns."
And something in Donnie's chest did a worthy ninja flip before his gaze flickered to Raphael who was rooted to his spot with the utmost amount of trepidations seeping through him. They shared a look before glancing back at Leonardo who was giving Michelangelo an incredulous look. Then when Leo opened his mouth, both Donnie and Raph immediately began to plead for their oldest brother to talking, but it did nothing to stop Leo from saying, "are you seriously comparing what I'm going through, to the time you found out leprechauns aren't real?"
And then their secret was out in the open and the only thing Donatello could do was hide behind his fingers while the horrified voice of his youngest sibling cried out, "leprechauns aren't real?"
Raph and Donnie were done for, and after silently communicating with each other, they bolted from the rooftop at full speed -planning to barricade themselves in their room for a day or two- and leaving behind a yelling Michelangelo and a befuddled Leonardo.
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Dialogue courtesy of season 1 episode 20 'Enemy of my Enemy'