Okay so to let you know, this is an Axis powers Hetalia (all characters mentioned belong to Hidekaz Himaruya) fanfic, the two main characters are Ludwig(Germany) and Gilbert(Prussia now east Germany)
They call each other west and east.

I didn't come up with the idea of RE_BORN (Prussia got dissolved and Gilbert returned as a kid to terrorize his brother).
the first RE_BORN fic from the original writer.
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It had been a long day, the meeting had, as usual, dragged on much longer than Ludwig intended to stay. The car clock told him that it was already midnight. With a sigh the tall blonde focused on the autobahn again. It would take another two hour drive to get home, where a sleeping Gilbert would lay on the couch. The child always tried to stay up for his brother. It was sweet, but Ludwig knew it would get to the small body someday. He had told his little bruder to go to bed at eight, but Ludwig always ended up carrying the child to bed.

Sighing once again the man rubbed his tired eyes. Not even the radio seemed to provide good company, since it was playing slow songs that made the German feel even more sleepy than he already was.

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"ah almost home." the German sighed in relief as he turned a corner to get into another street, home was just two blocks away now. Happy that he was nearly there he relaxed a bit into the soft seat of his car.
When he stopped at the traffic light he did hear the sirens of the polizei, which made him wonder what was going on. He didn't really pay much attention and drove off when the light turned green. When the dark car was onto the middle of the crossing another car(which was the cause of all the commotion around the blocks) came through the red light.
Ludwig could barely react to what was happening. "I'm going to die..." were the first thoughts he had when the other car just drilled through his Mercedes. A couple of seconds after the accident Ludwig blacked out.
On the cross section of the road lied glass, scraps of metal, the polizei who caught the driver who caused the mess and called for an ambulance. Ludwigs head was cocked back in a very nasty position, blood was staining his skin, his clothes, his car. A large gaping wound on the left temple, his right arm twisted in a very unnatural way and his left leg...well...Let's say the surgeons would have a nice puzzle on that part of the Germans body. All that Ludwig could recall was a lot of bright lights, dulled sounds and some blurry sights of the Krankenpflegers, who were checking on him.
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It took a couple of hours before the polizei had managed to find Gilbert, since he was the only one registered as family of Ludwig. When they came to the door and rang the bell it took a while before the door was opened. Expecting an adult, the cops were surprised that they had to look down to see a child. “Excuse me, are you Gilbert Weilschmidt?” the female cop asked the boy as she lowered her self down to his height. The boy nodded slowly and sleepily. “Yes…What’s wrong?” he asked. Since he was sleepy and West hadn’t returned just yet made him calm and fairly polite. “May we come in?” the male cop asked, showing his badge to the boy.
The white haired boy opened the door further and allowed the cops in. “I’m not sure what you want but you better not touch anything, Bruder will be angry if you do.” He said as he slowly closed the door again when the cops were inside the huge house.
“Well…It is about your Bruder actually.” The male cops started but soon enough the woman took Gilbert to the living room and sat him on the couch, while she just stood in front of him. “He’s been in an accident and has been taken to the hospital.”
The child had blinked at them and snorted a little. "Haha, are you joking? Nein, that's impossible! Bruder West is awesome, he can't get hurt." the young boy had just chuckled that out, but understood the seriousness when the lady had knelt down to eye height and looked him straight in the scarlet eyes.
When the boy understood that it wasn’t a cheap joke, tears began to fall from his eyes and he clung onto his teddy rabbit, which had been next to him the entire time, holding the thing close to his chest. It didn't take long before he began to wail that he wanted to see his bruder, wanted to be with Ludwig.
After a short discussion the cops took the boy to the hospital, where nurses took over the care of the boy. He was explained to be quiet and careful with the big man and that his bruder was tied to all sorts of tubes and machines that would be a bit scary. The boy heroically had nodded and held onto Birdie, he wouldn't give a hand to the nurses, he wouldn't.

Slowly the boy walked into the IC and took a deep shaky breath. Bridie was balanced in his elbow as he slowly approached the high bed. All the machines made odd noises that did scare the little boy a bit. But the man that was on the bed scared him even more. All he could see from the ground was a man with blonde hair, being stitched up, bandaged and had casts around his right arm and left leg.
"He's awake, you can talk to him, but he can't talk back." a nurse said to the boy when she picked Gilbert up and carefully placed him on the bed beside Ludwig, making sure he wouldn't block off the tubes. The young nation looked at his big brother, Who looked back with half lidded eyes. The scarlet eyes soon tear up again and he sobbed softly. "B-bruder..." he sobbed softly as he carefully lay down to hug his big brother. Ludwig couldn't move that much, but he did manage to lay his left bandaged hand on the boys back, rubbing it weakly. The blue eyes that usually were so stoic closed, tears fell down his cheeks and onto the boys hair.
As soon as Gilbert noticed that he sat up again and wiped away the tears from his own face with his little fists. “Don’t cry, Bruder West…You’ll get better!” the boy promised, trying to be strong for Ludwig.
The man opened his lips to speak, but he couldn’t get out any sound. All he wanted to say was that things would be okay soon, that he would be home again…But his voice just failed him. With a deep sigh he looked at the boy who was just staring down at him. Now he could finally understand how Gilbert must have felt when he was injured after battle.

The young boy soon enough patted the man’s hand carefully. “I’ll take care of you.” Gilbert promised the man with a sweet smile. “And Birdie will watch over you.” The boy got the stuffed rabbit and put it besides Ludwig’s head. “There.” The boy said softly. “Be kind to one other okay?” he asked before he looked at his bruder and sniffled slightly.
All the blonde could worry about was who was going to take care of Gilbert now…No one except Arthur knew about Gilbert. And a hospital wasn’t a place for Gilbert, he’d get bored and would go exploring, causing the nurses trouble. Ludwig knew that, but…Maybe…Just maybe Arthur wouldn’t mind watching over Gilbert, zjust until Ludwig would be fired from the hospital.