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It’s not like they set out to have a secret language; yes, technically Alex had learned Kryptonian for that very reason.
This was something different.
It wasn’t like no one else could understand what they were saying, it was more like they were speaking in code.
A dizzying mixture of secrets one only shares with their sibling and inside jokes sprinkled with a serious dose of ‘don’t tell mom’.
“Lexie, do you remember that one time in the barn...?!” Kara would begin, face red with laughter long before she had shared any pertinent details.
“Oh my god! How could I forget?” Alex replied, equally amused much to the dismay of everyone else sitting around Kara’s living room for game night. “If mom ever found out...she’d still kill us today!”
The siblings dissolved into helpless giggles, completely oblivious to the fact that no one else had even the slightest idea what they were talking about.
Except J’onn. Because he could read minds; actually only Alex’s mind in this instance and the narrative he picked up on was slanted at best, predictably one-sided.
No matter what shenanigans the Danvers had gotten up to as kids, Alex always found a way to justify the destruction and Kara dutifully backed her sibling up because she’d never had a sister before.
Because everyone she had known and loved was lost in one spectacular, cosmic explosion and what she had built with Alex was more than her orphaned, teenage self had dared hope for.
Because Alex was a nerd of the highest order and the majority of their childhood adventures revolved around Alex trying to figure out exactly how alien her new sister really was.
And Kara was just as eager to know more about her strange new abilities.
After all, on Krypton she was a regular teen, fragile and non-descript as Alex was now. There hadn’t been anything particularly special about her and had things not gone so inexplicably wrong, she would have lived a typical life.
Now she had abilities that most of the planet could only dream of. She could do things that she herself had never imagined so if her new sister, along with a healthy dose of scientific experimentation could help her make sense of all this, so be it.
So there was the fire in the barn, to see if Kara could feel heat or at what point she might begin to burn. She couldn’t and she didn’t burn but the new clothes Eliza had just bought her lit up spectacularly!
As did the back wall of the barn. Oops!
Then the duo had wondered, if Kara was impervious to manmade heat, what about her heat vision? More burnt walls and a small-ish forest fire in the creek behind their house.
The next experiment involved dry ice from the school lab because if Kara couldn’t feel heat, was she equally impervious to the cold? Only one way to find out!
Eliza had been understandably perturbed when she’d taken Alex to the doctor for a cold burn on her hand in the middle of July in California. The eldest Danvers had claimed it happened during an experiment at science camp, not from sticking her sisters hand in a tub of dry ice. Neither girl thought their mother was fooled but Eliza let that one slide.
The test of Kara’s strength, basically Alex tying dozens of pillows around herself while Kara squeezed as tightly as she dared, resulted in the future agents first set of cracked ribs but definitely not her last.
Again and again, the siblings need for scientific discovery resulted in holes in the drywall, noise complaints from the neighbors, countless trips to the emergency room for Alex and after one particularly disastrous mini-explosion, trying to explain how a Kara shaped hole ended up in their screen door and the oven in the front yard!
After that, Eliza stopped them every time she had suspected they were discussing a new experiment, a new way to test Kara’s abilities, so the girls began speaking in shorthand, a habit they carried well into adulthood.
A surly, vaguely disgusting alien who had decided to tear up a good portion of downtown National City effectively ended game night. Supergirl had been the first on the scene yet hadn’t been able to contain the beast. When Alex rolled up in the DEO tactical van, Maggie in tow because the detective was practically DEO at this point, she knew she had to help her sibling.
“Supergirl!” She yelped as Kara slid to a stop a few feet away from her, the blonde gingerly popping her jaw from the blow the other alien had landed there. She quickly pulled her sister to her feet.
“I don’t know what else to do Alex! I’ve hit him with everything I’ve got already, he’s too strong!” Kara all but whined, not used to being unable to best her adversaries.
“He’s too strong...” Alex repeated, lost in thought for a moment. “Of course! Kara, what was the very first thing I taught you in the green room?”
Kara’s eyes widened in understanding. “You think it could work?”
“Worth a try. What else have we got?”
“But the civilians...”
“On it! Maggie,” the agent whirled on her confused girlfriend. “Clear this area. Get as many civilians to safety as you can.”
“What are you gonna do?” Maggie asked as she relayed the orders to the agents nearby.
“Something you’re not gonna like...” Alex muttered before charging towards the rampaging alien!
“Alex!” Maggie cried in panic.
“It’s okay!” Kara assured her as she took the air. “We got this!”
Maggie was unconvinced but she resolved to trust the sisters, still having no idea what the actual plan was beyond Alex doing something incredibly dangerous and Kara backing her up.
“Damn, this guy is fast!” Alex muttered to herself as she continued to zig-and-zag through the carnage littering the city’s streets.
Occasionally, she would turn and fire on the creature just to ensure he continued to follow. Not only was he following but he was quickly closing the gap!
“Supergirl!”
“I’m right above you!” Came the equally concerned reply. “Take your next left and get ready to duck!”
“Got it!” She turned the corner, nearly colliding with a wall when she realized she was barreling down an alley with no outlet! “Kara!”
“Drop now!” was the only response and the agent hastened to comply, skidding to a stop, arms covering her head as she braced for impact.
Alex vaguely registered her sister appearing at the end of the alley, legs set apart, bracing for the incoming alien. The agent quickly rolled to the side, pressing herself tightly against the wall as the alien found itself barreling straight into Kara’s outstretched fist! The resulting impact sent a sonic boom that could be felt four blocks away as the alien sailed through the air before landing in a heap on the next block, motionless.
“Yes!” Kara cheered as she pulled Alex to her feet.
“Nice work, sis!” Alex beamed, holding her hand up for an obligatory high-five. Kara slapped the agent’s hand with a little too much force, not realizing her mistake until her sister winced. “Hey! Watch it with the super-strength, will ya?”
“Sorry!” she replied sheepishly. “Guess I’m still a little pumped!”
“Alex!” Both women looked up to find Maggie and J’onn rounding the corner with concerned expressions. “You guys okay?”
“Yeah, babe, I’m fine.” Alex replied with a rueful smile, still flexing her sore hand. “The alien?”
“Contained.” J’onn replied, trying not to smile because their “plan” had been reckless and totally not a plan at all. “How did you come up with that on such short notice?”
“That was easy!” Kara grinned. “When Alex first started kicking my butt in the green room, she told me ‘always use your opponents strength against them.’”
“So all we needed to do,” Alex piped up, “was draw him away from the public so Kara could give him a taste of his own medicine!”
Maggie gaped. “You got all of that from like two sentences?”
“Yep!” the siblings agreed as they tugged the detective along towards the tactical van, their only thoughts of pizza, ice cream and pot stickers while J’onn trailed behind them shaking his head.
“Nerds.” He heard Maggie mutter under her breath and his smile widened ever further.