Mycroft Holmes can remember all the awful things Sherlock has done to him. His younger brother has shot Charles Magnussen, broken into top-secret military bases, and stolen confidential government files. If one were to ask him the worst thing Sherlock has ever done to him, he would answer with one of those, as they were his top three.

However, none of them were truly the worst.

The worst thing Sherlock ever did to him didn't even happen recently. It happened when Mycroft was a fresh ten years old.

Sherlock was two, almost three, toddling around on his too-large feet and matting every food within reach into his dark curls. Mycroft never liked his younger brother, as he was a sniffling, sobbing, slippery mess. Why anyone would willingly bear a child to then have to take care of its every need was beyond him. He was absolutely convinced that he had been the perfect child, never crying or sniffling or sobbing, because there was no way that he had ever been like his little brother Sherlock. Even his name was atrocious: William Sherlock Scott Holmes, however Mummy merely called him Sherlock. He had been pink as a baby, looking vaguely like a shriveled alien. Mycroft hated holding him. It was never much of a problem, avoiding the child, until he began to walk and talk.

He would follow Mycroft everywhere, calling the name, "Mikey!"

That was not Mycroft's name.

Time upon time again, he endeavored to teach Sherlock his proper name. "Mycroft," he would say forcefully. "Not Mikey. That is not my name, Sherlock. How would you like me to call you Sherly?"

Sherlock merely gazed up at his brother with large, confused eyes. Mycroft sighed in exasperation, abandoning the feat until a later time.

"It's Mycroft, Sherlock!"

"Mikey?"

"No, Mycroft!"

"Mikey!"

Mummy tried to explain to him on several occasions that Sherlock was still a tyke, therefore he wasn't ready for big words yet. However, that never eased Mycroft's frustration when his younger brother called him by the atrocious nickname "Mikey." It was not his birth-given name, therefore he should not be called it. How could Sherlock not understand it, despite all of his attempts at telling his it wasn't his name.

Despite a nuisance child growing and thriving in Mycroft's home—because it had been Mycroft's home first—Mycroft remained devoted to his studies. He was years above others his age, and was well on his way to moving ahead to Uni in a few years. He already knew that he would attain a high position in the British government in the future, possibly even Prime Minister. He had no doubt that he could make it that far if he wanted to.

He had learned Serbian in a matter of hours last week, and had mastered Romanian this week. Languages came simple o him, as did mathematics, history, and literature. He'd heard his father describe him as a prodigy on one occasion, and Mycroft couldn't help but agree. He knew more than Mummy and Daddy combined. They were both imbeciles next to him, and he was only ten years old. He often marveled at how dull they were, and how two people such as them could create a genius such as him.

He valued no one other than himself. Others were a waste of time when he had a bright future ahead of him. As was his motto, "Caring is not an advantage."

It was on a lazy Saturday evening when that changed.

Mycroft was examining the paper, deducing in mere minutes the "spontaneous human combustion" case (it had really been a case self-immolation, the man had been protesting some law or other, and decided to make a statement. It was a rubbish statement, however, because no one but Mycroft spotted motive behind his death). Suddenly, the newspapers were torn violently from his hands, and round, blue eyes were staring into Mycroft's. Mycroft shifted in his seat, but Sherlock obviously took that as an invitation to climb aboard his lap.

"Mikey?" he said, soft voice raising as if asking a question. Mycroft saw the childish inquiry in his narrow features. "Whadda you doin'?"

"Sherlock, if you cannot speak to me in full sentences, do not speak to me at all," Mycroft snapped firmly. "I'm busy."

"Bu-see?" Sherlock repeated, lips separated in silent wonder. He pensively gazed at Mycroft, as if asking his older brother to open up the world's wonders and share them with him.

Mycroft sighed. "Yes, busy! Now scram, Sherlock."

Sherlock did not move from his perched position. Mycroft squirmed uncomfortably. "Mummy tol' me to pway wif you," Sherlock said. His childish language drove Mycroft to near-insanity.

"Mummy was wrong, so go away!"

Sherlock's angular knees were digging into Mycroft's ample thighs, and his spindly hand found their way to clasp Mycroft's shoulders. Sherlock was frowning, head tilted to the side. "But I nee' someone to pway wif, Mikey!" he cried, lower lip beginning to wobble threateningly.

But Mycroft only got more upset. "Do not call me that!" he iterated. "My name is not Mikey, just as yours is not Sherly."

Instantly, the tears disappeared from the toddler's eyes and he repeated with a grin, "S'erly?" The little boy giggled, causing Mycroft's chest to tighten with an unconventional tenderness. "Mikey, you funny!"

Mycroft's eyes darted around, unsure of what was happening. He'd been in the middle of scolding his younger brother for his improper language, but something had occurred. Mycroft hated Sherlock, but when the child smiled at him like that… It was as if he'd gained access to Mycroft's world. The world that no one was allowed into but himself.

It was the first time he'd ever felt feelings for another person in his life, and it was horrible. But he couldn't stop caring for his little brother. It felt like his duty.

Even years later, at the head of the British government, he loved his brother to a fault. "Caring is not an advantage." No, it was not. But that simple action, a quick smile from his two-year-old brother, had been the worst thing Sherlock had ever done to him.

It had caused him to care.

This has been asking to be written for a long time now, and I finally got around to it. I'm a sucker for Mycroft, so I hope you enjoy this as much as I did! Please take a moment to leave a review!