Mycroft was always the lonely child. The outcast. The freak. For why exactly, he didn't know, but the fact he carried an umbrella everywhere with him didn't exactly help. Even though he never had any real friends, Mycroft didn't care. He had Sherlock. Ever since he could remember, he was extremely desperate for a brother. All the kids at school had one, and Mycroft wanted one too. It was too late for a big brother, but he decided he could settle for a little one instead. Even though he'd eventually got his wish of a sibling at the age of seven, he grew up confused as to why he could only remember certain parts of his brother Sherlock's childhood.
When Mycroft eventually asked his mother and father why his memories of Sherlock were so patchy, his mother simply smoothed his dark curls back and answered, rather sadly, that he had been ill for a long time, and that sometimes he could get confused. Mycroft simply replied that he felt fine, not ill at all, and left it at that. When Sherlock started school, Mycroft took it upon him to look after him as his classmates elder siblings had when they were young, and would always watch out for him. To his dismay, Sherlock seemed to have almost the same social skills as him, and would always wander around the playground by himself. Mycroft decided to take advantage of the situation and he and Sherlock would often walk around the playground together talking and laughing, although they received many strange looks from the other children, yet again for reasons Mycroft was unsure of.
A lack of social skills wasn't the only thing Mycroft and Sherlock had in common. Sherlock was also tall and skinny, and had the same wild dark curls. They both shared a passion for science and psychology, and each preferred their own company, so it wasn't just their appearance that made them alike. Yet, despite all these similarities, Mycroft and Sherlock still had their arguments. Sherlock never initiated these arguments, always Mycroft, and these varied from whispered heated debates to full on screaming rows, depending on how he felt. While Mycroft could barely remember what any of the arguments were about, he could never forget the look on his mother's face when he shouted at Sherlock. A look of conflicted agony and confusion, and like the isolation from his classmates and the strange glances he often received, it was another thing that deeply confused Mycroft, but just ignored.
As he and Sherlock grew older, Mycroft started to notice significant differences between his brother and his self. While Sherlock continued to grow taller and taller, Mycroft never made it to six foot, and swore he was shrinking. As Sherlock stayed skinny, Mycroft ended up getting slightly pudgy, although his mother assured him it was from the medication he was still on from his mystery childhood illness, and his chubbiness could go away any day. And finally, as Sherlock's dark curls stayed intact, Myrcoft slowly started to lose his hair. These new found differences, as well as Mycroft moving out, drove a wedge between the brothers, and for years they barely spoke, although Mycroft did secretly check up on Sherlock from time to time. He grew increasingly worried as Sherlock failed to make any friends or even acquaintances, and when Dr. John Watson appeared in his life, Mycroft couldn't believe the coincidence. John was everything Mycroft would have looked for in a friend when he was a boy, and hoped that Sherlock secretly thought that too.
After years of isolation and loneliness, a friend had appeared out of thin air. Mycroft watched as the two men moved in together, set up their own consulting detective agency, which was something Myrcoft had always secretly wanted to do. This made Mycroft realise that maybe he and Sherlock weren't so different after all, and decided to reconnect with his brother and John. For a while everything was okay. Then Sherlock died. Completely out of the blue. Mycroft had never experienced pain like it. It was like he'd lost a part of himself. But no one took it harder than John. Mycroft would never forget the memory of John clasping the smooth marble headstone like he could never let go and silently sobbing for Sherlock to c-
"Mycroft?"
Mycroft's eyes opened as he jerked upright. With bleary eyes he looked around the unfamiliar room in panic. Where was he? What was going on? Slowly the pieces came together. The strange looks. The mystery illness. A blurred childhood. Sherlock being everything Mycroft ever wanting to be. Sherlock. Sherlock. Sherlock. He grasped the arm of the chair he was sat in, and with shaking hands reached out for the glass of water next to him. A middle-aged woman sat opposite him with a notebook, tapping a pen against a page with ominous looking notes. She looked at him, frowning a little.
"You spoke about a Sherlock?"
Mycroft nodded.
"And he died?"
Another nod.
"Did you know him well?"
Mycroft opened his mouth to answer, and realised no words would come out. When the woman leaned further forward and started to ask again, Mycroft interrupted her.
"Of course I did. Sherlock," he choked out,
"Sherlock is, WAS, my..."
He couldn't say it. Saying it would make it real. But he knew if he didn't, this interfering woman would just keep bugging him until he was forced to. So he took a deep breath, and tried to keep back his tears.
"Sherlock was my imaginary friend."
There. He'd said it. The woman widened her eyes.
"Your... imaginary friend?"
He nodded.
"I was alone all through my childhood. I wanted a friend. A brother. So I... created Sherlock. He was everything I'd ever wanted in a brother, and everything I'd ever wanted to be. But he was simply my imagination."
The woman leant back in her chair.
"And he 'died'? He's gone?"
Mycroft nodded again, this time a single tear slowly made its way down his cheek.
"Yes. Yes he is. Forever."