Real Life in Four Dimensions

Jump. Just do it.
Kiri leaned over the the cast-iron balustrade, the sting of exhaust on her face. Grease and flecks of metal were under her fingertips, and the sunset was spilling onto clouds of smog. The sounds of engines in the sky and gyros on the ground were blanketed in the falling light—as if ultraviolet affected the air.
Stories below and far away, the airfield spread its wings. Long distance shuttles touched up and down on the landing strip, little lights blinking madly on wingtips and exhaust rippling in the sky. Ads glowed along the wall closest to her. As images slid in and out of on another, their collected glow making her turn skin vile shades of pink and green. She held up her head to the sky, and felt it curl through the  strands of her hair and onto her skin—this was a good time to jump.
She peered directly below her at the flurry of passing cars; they sped along tracks. A train track  snaked above them, curved and smooth; its pillars jutted into the ground. A bullet train came past then, sending a rush of wind at her face.
That swoosh of oxygen kicked the dopamine sectors in her brain into gear—it was enough to make her push herself over the edge. She slipped over in one motion, keeping back the instinct to huddle down on the platform in fright. Her heart jumped up in her chest as her body cut through the air, and the lines of cars below zoomed closer with the tick of each millisecond.  
There was a hum and a swoosh as the thrusters attached to her boots pushed back with equal force, and in the time she had been falling, she was already fifty feet in the air. The thrusters were thick, metal braces  that locked into the soles of what appeared to be heavy-duty combat boots. The thrusters pushed back on gravity from all sides and propelled her through the air. They were ugly and monstrous, and there was always an the danger that they would just sputter out and drop her to the ground, but she could no longer imagine a life without them.
Kiri held pressure switches between her gloves, and with the slightest  touch and movement of her body, her boots responded with addictive satisfaction. A smile with more light than the  dying sun crossed her face. Bending forward, she sped through the infectious air. The wind curved around the skin bared by her shorts and cut into the cotton of her shirt as she flew at twenty, then sixty miles per hour. Bands of fluorescent lights and video ads reflected in her goggles as she dodged between the rivers of cars, under the metro tracks, and around the sharp corners of buildings. The air was cool and static in the increasing darkness, and a muddy twilight soon changed to a rainbow nighttime. She was her own entity in this sprawling microcosm, untethered and hyped with adrenaline. The kind you cannot buy. The kind that flying gives you.
She boosted higher into the air, past other, lesser modes of transport, and over the roofs. The wind of her passing rippled the laundry hanging along rooftop gardens. She dipped low over a group of kids playing between the pipes and corrugated iron. They were scrawny things that jumped in the air. With their arms stretched, they called laughing as she passed. A mother dropped her washing into a bucket and shook her fist, as if to scream—there are laws against that  sort of thing! Kiri guffawed and veered away, ducking over an uninhabited rooftop.
The city rose stark and vibrant, all below and around her. The oxygen buzzed and burned. The lights danced, and the engines whirled. Even the air seemed to brim with an over-abundance of electrons, and as Kiri allowed herself to come to a hover, it felt as though it was those particles that carried her.
Something shot past her, sending the very pollution out in torrents.
Another buzzer had come to a hover fifteen above her. His hair was whipped with the same wind that flushed his skin and tousled his t-shirt, and his eyes were hidden behind a pair of goggles that sent Kiri's own reflection back to her. He wore a goading grin that told everything about what was going to happen next.
“Did you have to buy kid's boots so they'd fit on your feet?” he wanted to know.
Kiri brought herself up so that they were facing each other, and replied, “Five bucks says they're faster than the garbage you've got strapped on.”
Like Kiri, this buzzer had obviously done some modification to his thrusters. He had hazard  lights attached to the them, so that the power-cells appeared to glow green.
The grin flipped to a smirk and he said, “You've got a deal, little sister.”
Before he could put a period on his sentence, they had already sped off. There was no particular direction in mind—just trying to beat the air before the other. Kiri took the lead, speeding past a seventy foot advertisement—like a bug to a television screen—and then she lost him. Her momentum faltered in the slightest of instances as she tried to relocate her adversary, and in that moment he sailed over her head, letting out a laugh as he did. Kiri kicked herself back into gear, and the world spun around her. Her focus was of the utmost seriousness as she exacted all her attention on the orange and of his shirt and glow of his boots. She hair-pinned around metro-track pillars and rocketed back towards the sky after him, but he was already too far ahead. By only twenty feet, but it was enough. She was going to loose him.
She spied a shortcut.
Kiri dipped out of sight, and followed a tenth-story pedestrian platform, never getting too close until the last moment. She then cut across the platform and into a tunnel. Totally illegal. The tunnel was alight with moving video advertisements, and people ducked and shouted as she flew overhead. The wind sucked through like a multi-colored vacuum, and within seconds she shot out to the other side.
“Not your sister!” Kiri called as she passed the second buzzer.
She did not miss the shock on his face as she overtook him, shock that shifted right back to amused determination. He was now forced to follow her).
They sailed past the pixel screens and concrete gardens, and up towards the stars that tried and failed to poke through the sky. Police officers eyed them from where they sat on clunky hover-bikes. The buzzers slowed their speed and laughed at one another's innocent faces until they had passed the cops, and sped off again. This could go on for ages.
The boy seemed to recognize this, for he yelled  to her, “First to the top of Port Tower wins, yeah?”
“Yeah—!”
With its sleek edges, like some giant otherworldly sentinel, Port Tower was the highest building for miles. It had become apparent to Kiri that he was as familiar with these open air streets as her, and as they took off in the direction of the tower, Kiri knew she would have to do something extra to win. Would he have the guts to follow her, though? Kiri's smile came to her face—probably not. She could already see him making the moves to take a quick rout to the tower.
But, not the quickest.
Kiri made and abrupt u-turn, and he understood what she was about to do. He faltered slightly in the air, having already begun down the path he had chosen, but Kiri did not wait to see if he would follow. Within moments, she  passed over the gates of what had been dubbed locally as “the cesspool”, a giant inner-city chemical dump. It was a ghost town, run-down and no longer operational. After a huge legal dispute, ChemLife had lost the rights to the place, but the plant had been yet to be torn down.  Kiri was already passing over the corrugated ceilings of empty buildings and over stagnant vats of goo. Towering and rusted cranes, arms, and pinchers rose out of the concrete. As she flew past those weird, metal towers, bits of red flecks came off with her. They groaned and creaked in the night, and the lights of the city around her seemed to dull as she cut deeper into the plant. She swore the goo glowed.
Halfway into the plant, she heard something new, a whirling and clicking. Kiri allowed a backwards glance to find two patrol-bots coming up fast on her tail. They were streamlined and powerful with crimson eyes for added effect. Their bodies were  bulky, but they cut through the air with ease. The 'bots were a strange juxtaposition to what they guarded, but Kiri's mind was far from this comparison. She was busy doing the only thing she could: evade.
The robots barked at her in calm and urgent voices to halt! and  that there was no trespassing permitted! Kiri wove around the stagnant giants at a  breakneck speed, for once out of the plant, the robots would not be able to follow her. She merely had to get out. With their pre-programmed warnings failing them fast, the gears and plates on the 'bot's arms realigned themselves, revealing built-in stun guns. Kiri only had to hear the sound of the barrels fizzing to know to begin zigzagging through the air. They began to shoot, and she was attempting to make her patterns as unpredictable as possible. The 'bots were deadly silent now as all their circuit boards focused on one thing: knocking her out of the air. Kiri squealed as a dollop of freezing solution smacked against an array of cords, nearly hitting her head. Another slipped by  her torso.
She glanced down at the vats of goo. If her boots were hit, the freezer would destroy the insides of her thrusters, and she would dive right into that mess. Oh God.
It was alright, though. She could do this. Kiri bent forward as far as she could, attempting to allow the air to pass her as easily as possible. Her thighs were beginning to sting with the effort.
A third and fourth 'bot came from the shadows to join the chase—accompanied  by more clumps of freezer shooting passed her. Kiri nearly veered into the piles of machinery more than once to escape it. She could make out the edge of the compound rising up in the distance, the city lights shining like exit signs. The piles of freezer were coming faster now, and doubt flitted through her mind.
Their voices called out, “Halt—!”
Wait a second...
The sound of thrusters bounced off the rusting metal as the second buzzer dipped into view. “This was so dumb of you,” he scolded, and soared in an arc away from her, drawing some of the patrol-bots to him. As a new trespasser, the 'bots were limited to yelling at him for now. Kiri wasted no time using his distraction to navigate out of the compound. She bolted over the fence and back into the city-light, throwing up her arms and letting the enthrallment come out in a yell. Seconds later, the second buzzer soared over and came to a halt near her.
The 'bots stopped at the edge of the fence. They sat there for a moment before fading back into the plant. Something that hinted on disappointed seemed to emanate from their blank faces.
“That was so stupid,” The second buzzer repeated, crossing his arms and slowing to a hover.
“That was so awesome!” She corrected, triumphantly pivoting in the air.
The stern expression flitted away from his face and he smiled. “Don't speak so soon,” he warned, and shot back into the sky towards Port Tower.
Kiri shot after him, her exhaustion forgotten. She could hear him yelling to her as she closed in. The lights streaked in her peripheral vision as they wove to the base of Port Tower. The massive construct was suddenly before them, and they shot straight up the incline like rockets. Their reflections were blurs and the city a kaleidescope in the miles of metal paneling. Kiri lost him to another side of the building, and her face stung with the wind as she flew higher. Gravity was fighting her; she grit her teeth and  streamlined her body to fight back. The tower was slipping down like linen falling to her feet, and the smog-lit sky opened before her.
She came up to the tiered rooftop—just as he did on another side. Here the seconds counted. She extended her fingertips to the steeple moments before him.
She had won.  
Her opponent dropped his hands and groaned, and she spun around steeple, calling “Who is awesome now?”
He shut off his thrusters and plopped down on the uppermost tier. “That was pretty good,” he admitted, “But I would have kicked your ass if I hadn't blown so much stream at the chem-plant. Great going, by the way on that route-choice.”
“Whatever you say,” Kiri tittered as she mirrored his actions and took a seat on the steps. “But I still won.” The boots were impractical for anything but flying. With the thrusters shut off, their feet hung weighted and useless, gravity finally having its way.
Kiri tugged her goggles to the top of her head, and the view exploded into her vision. From this high point, the city sprawled out in all directions. Colored lights popped through the hazy air and faded into the distance, until they were all but beads. Their glow ignited the sky, turning it a shade that struck between purple and green. The city was a mass that seemed to writhe, and yet remain unshakable. Without her boots, Kiri was overtaken with a sudden sense of vertigo; the lights spun and she realized just how far they were from the concrete. It was miles down, and miles upon miles all around. It was a view that was both sickening and spectacular.
“Hey.” She turned to her partner. “Thanks for helping me out back there. That was some of the best flying I've seen in a while.”
He made a face that showed his continued disapproval of her decision, but she laughed at that and added, “I'm Kiri.”
She held out her hand, and he shook it. He had removed his goggles as well, and wide suction rings had been left around his eyes. Tufts of his hair stuck out in all directions.
“4-D,” he told her.
“4-D, what?”
“It's my name.”
Realization dawned and she said, “That's pretty sweet. Lovely to meet you, 4-D. Sorry about beating you, I'll take it easy next time, yeah?”
He raised an eyebrow. “Oh really?”
She grinned. “Yes, really.”
They stared one another down for a moment, and then 4-D asked, “Are you hungry? Would you like to get some dinner or something?”
“Only if we race there.”
“Oh,” he helped her to her feet, “We're racing, little sister.”
And they jumped out into the sky.