When he was young, very young, Dee Dee would often drag him into her games. These included but were not limited to, tag, hide n seek, house, school, and doctor.
She loved playing doctor.
She would pinch his nose and then pretend that he needed to visit the doctor, which was her.
She was forced to stop playing her favorite game when she actually ended up hurt Dexter one time, leading to him crying on the floor with a small cut on his hand. He doesn't quite remember how the game escalated that far, but he remembers Dee Dee actually apologizing to him sincerely.
The next time the game of doctor was played was merely a year after that. The lab was well into construction at the time, and a much less careful sister of his went around galvanting in the construction zones. She ended up scraping her knees pretty badly, and Dexter was then forced to think of different medical supplies for different emergencies. Dee Dee was fine, like she always was, but Dexter couldn't help but notice how she seemed to dance around danger from that point on.
The years that followed, more injuries were acquired. The two siblings had become experts at patching each other up, to a point where their mother was surprised that Dee Dee correctly popped a joint back into place that had been causing her back pain for years. The parents thought their kids were just natural born doctors, but they knew better. Or at least Dexter did.
And this was the routine for quite a while, all the way up to when they both moved out of the house.
And then it stopped.
Dexter, or rather Twelve, seemed incapable of repairing himself as he once did. This left the long gashes on his back to blister and scar over, leaving strange grooves in flesh where stitching should have been applied.
He regained his doctor skills to an astonishing degree once the world ended. Under Mandark's rule, nobody knew how to heal the sick. Or bandage cuts. Or be healthy in general.
He tried his best to teach them.
He gently ran the stethoscope over the child's bare chest, listening to the rapid heartbeats. The child, a girl who never learned how to speak, was running a fever. It was the flu. He stayed with her, giving her water from his bottle and cooked food when she was awake. He handled every pregnancy the same, approach the mother and make sure it was actually a baby inside her. If it was, he'd leave the mother alone, but more often than not there were strange worms or tumors inside people that made their bellies bulge.
He did surgery on those ones.
And sometimes he simply brought food to the starving, and water to the thirsty. He checked their pulses, their tongues, their breath and their teeth. He inpected them all, making sure that there was no plague that would spread and kill off the rest of the human race. It became routine, so much so he was honestly surprised with himself.
He though back to when playing doctor was simply that, a game to play. Now that game had expanded and people's lives were on the line.
He looked down at his tattered white coat and the small box of medicines and ointments in his hand. He looked at the stethoscope and realized that he was an actual doctor.
The girl in front of him wheezed while she breathed, and Dexter checked her temperature again. It had lowered, to his relief. He wasn't quite sure why he was adamant about healing the sick. He asked himself this often, and the answer was usually "to keep the rest of humanity safe". But he knew that was almost a lie.
Almost.
It was important to keep humanity healthy, yes, but he just couldn't handle the guilt if he didn't help.
He tried once. He was about to leave a sick woman, someone hauntingly similar to someone he used to know, behind to die. But he just couldn't do it.
Maybe, despite his new strength, he had grown soft.
He was just glad he could help.