This is an entry for Finish the Story Contest - WEEK #21.
Here is 
In the scant shadow of the guardhouse, a greenhorn Border Legionnaire was waiting for the end of his first watch shift, gasping for the heat.
Below him, there was the stretch of sandy desert that the XIX Floating Fortress patrolled incessantly, moving back and forth in the sky like a surreal and phlegmatic cetacean, with the low and incessant buzz of the managems that powered it.
Behind the line of Fortresses, the Lands of Man ideally began. In that marginal strip, there were meager pastures and stretches of scrubby bushes, attacked for miles and miles by a fine sand, like yellowish talcum powder, that made the desert gain extension every year.
"This year the wind has put so much sand down," the marshal told him, biting a gray mustache, one of the last days before the Duty Beginning ceremony. "And behind the sand, the Those arrive".
He was glad he no longer had just a stunner to defend him from the Those, like the guardians of the border in former times, before the Legions. Once, it was thought to direct the Those into reserves to prevent them from doing too much damage with their insatiable hunger, but then they started to run away, to strip the flesh off every head of cattle, to waste fields and orchards, to devour even the people... and more and more came from the desert.
He had been among the first in his draft class in combat and shooting exercises, but in his heart he was afraid of when he would found himself in front of a real That, and not an illusory image created by the trainers. It took him months to get used to the slouching and snappy movements of those lean and black illusions, all teeth, which he found horrifying.
During that first day of service, however, only an armored convoy had passed, transporting ordered and dull clusters of goleminers to the mysterious and vital mines of managems, on the other side of the desert. The Those did not find goleminers edible, luckily.
The Horn of Danger snatched him cruelly from his thoughts. Intruders in the fortress! How did they get in? How did they pass under our noses?
He grabbed the heavy terminator and ran down the spiral staircase, toward his team's collection point, his heart in his throat.
A scraping noise from a corridor to his right made him stop. Pointing the terminator in the dark, with a trembling grip, he shouted "Who goes there?!?"
The Those came out, completely different from the illusions of the trainers...
And this is my ending:
Is this how civilian life is like now, wondered the Border Sergeant.
The manatrain ride had been hellish. He only wanted to get home, shower and sleep. But he was still wearing the uniform, the Medal of Valor burning a hole in his chest. Of course, a reporter would notice.
Now there was a floatcam hovering around, green light casting the recording spell on his face. He was tired, and her questions kept coming.
"...are you going to apply for another term of service?"
"Still thinking about it."
"Do you agree that the overuse of goleminers is increasing the desertification?"
"I'm not an expert. I heard climate magicians are divided on the matter."
"Are you familiar with the name 'John Harper'?"
They were alone in the office. The Colonel asked, "Tell me again why you shot Captain Harper."
The Border Legionnaire looked down. "He... He took off his helmet and dropped the terminator. He started running towards the Those, waving his arms at us, he ordered us to stop firing--"
The Colonel stopped him. "Directive Eighteen."
The Legionnaire answered automatically. "Any Legionnaire demonstrating lack of conviction or dereliction of duty in the presence of the enemy shall be considered a threat and if possible, placed under arrest."
The Colonel nodded. "If possible."
The Legionnaire kept his voice steady. "Am I in trouble, sir?"
The Colonel smiled curtly. "No, son. If anything, you're getting a promotion. Your resolve that day saved the XIX. You did your duty, and thanks to soldiers like you, I have no doubt that we will emerge victorious..."
"...no," answered the Sergeant.
"Concerning the reserves scandal--," she began.
But he had enough: "Stop it."
"Excuse me?"
"Why!" he exclaimed. "Why are you doing this. You must realize that the Legions are protecting everyone! We are mankind's line of defense. If the Border falls..." He shook his head. "The Those hunger."
She stared at him long and hard, searching for some kind of understanding, but she wasn't able to find any. With a gesture, she turned off the recording spell. "Borders aren't a real thing," she said. "They are fiction. Pretense. We arbitrarily decide: this side can eat, that side must starve. So we draw an imaginary line like this" and with her foot, she traced a line in the ground between them, "separating ourselves from the monsters."
The reporter turned around and walked away, the floatcam behind her like a well-trained pet.
The Sergeant said quietly: "I'm no monster" and went home.
That night he dreamt of his first kills.
Pointing the terminator in the dark, with a trembling grip, he shouted "Who goes there?!?"
The Those were standing together, a huddle of bodies and fabrics and sharp blades. Their faces had the wrong color and misshapen features. The eyes were glassy, devoid of expression. They seemed famished, hostile and desperate. The way the smaller ones' skeletally thin arms, clung to the bigger ones, reminded him of... something.
Not people.
Nothing like people at all.
