Contrary to popular belief, his brother visiting was mostly a joyous occasion for Sherlock Holmes. Well, that is, if he had gained any weight. If he came to Baker Street with a freshly tailored suit and smug look on his face, Sherlock simply knew the visit wouldn't be any fun. Luckily for Sherlock, Mycroft didn't lose weight too often. No, Mycroft would keep his weight at bay for a few months -if he really tried- and after that he would simply give in to his greatest weakness and eat himself silly, until pants and shirts and belts had to be hidden in the back of his closet or thrown away in shame because they would simply not fit anymore. Sherlock adored not seeing Mycroft for weeks, because then he knew that he was hiding from him, and that the next time he saw him he would have added pounds and pounds of soft flesh to his ever-expanding waistline. Sherlock would then proceed to mercilessly poke fun at his older brother, who could not do more than silently and sulkingly agree with his brother's taunts.

Mycroft Holmes did the best he could to avoid these situations. He was on a diet more often than not and he would stick to it the best he could. The problem was that his 'best' wasn't even remotely good enough. A tiny wee taste of this here, a couple of these little harmless things there… Before he knew it he was right back where he had started and may be a little heavier too. He just couldn't resist food. His will-power failed him at the mere sight of fresh pastries, luscious desserts, succulent fat-filled meals... He just found everything to be so delicious! Mycroft was deeply ashamed of the permanent softness of his belly and he certainly didn't enjoy Sherlock's mocking, but if a three layer cake was at hand's reach that thing didn't stand a chance in this world. For a man like him, a perfectionist to say the least, this was a constant reminder of his flaws and limitations.

The next time Mycroft saw Sherlock he hadn't found the time to visit his tailor first. His trousers were digging deep into his midsection and there was no way on earth anyone –let alone Sherlock- could miss that sight. His brother was helping him with a case that seemed simple enough, but had demanded to see him in person to inform Mycroft of his conclusions. When he arrived, the half-contained smile on the younger man's face revealed such bliss that is was hard to overlook it. Mycroft braced himself.

-My big brother, I see life is treating you well.

-Marvelous, Sherlock. Do you have the documents?

-Why so eager to leave, Mycroft? Tea time doesn't come for another hour; I promise those cupcakes will be right there waiting for you when you go back to the office.

-I hardly have the time for your pestering Sherlock; do try to be more mature.

-Of course you don't, all that food's not gonna eat itself.

With a sigh, Mycroft snapped the documents out of his brother's hands and left the apartment. How the hell did he know he was having cupcakes with tea was beyond him. Oh, of course. It was Friday.

Mycroft had been extremely good with his diet lately. He didn't even cheat. Well, maybe once. Or twice. But he had managed to lose a couple of pounds and was feeling pretty optimistic about the whole situation. Sherlock thought otherwise.
When Mycroft arrived home that evening he found a little present from his brother. He usually sent him boxes of chocolates and refined pastries that Mycroft stubbornly ignored for a few days and ended up eating anyway, despite his best efforts. This time he didn't look at the package twice, though. Whatever it was, keeping it at home would be too tempting for him, so he grabbed it and threw it directly into his bin. He was proud of himself. So proud he even phoned Sherlock to tell him the good news.

-I thought you should know little brother, that you are wasting your money. That box you sent me has been discarded already. You should be more careful in investing your income since you clearly do not have a job. Not a real one that is.

-Lying is not becoming of you, Mycroft. And neither is your girth, in case you've forgotten... But then again, how could you?

At that point Mycroft just lost it. After all, he hadn't eaten any carbs or sugar in days.

-Why is it that you obsess with my weight so much, Sherlock? I cannot seem to figure it out. I have narrowed down to two options, nonetheless, either you mercilessly hate me or you simply do it for fun. Does it amuse you? Turn you on?

It was cheap, he knew it. Dumb and cheap. That implication was a new low for him and he would pay for it. So he waited. He waited for a witty response that never came. Sherlock seemed at a loss for words. After a few seconds of silence Sherlock simply hanged up on him.

A couple of days later, Mycroft showed up in Baker Street. Sherlock was facing the other way and didn't turn to face him when he entered the room.

-You have all figured out, don't you? Are you here to mock me? Tell me I'm insane?

-Where is John, Sherlock?

-I don't know, travelling somewhere. It's Christmas soon, is it not? I think he said something about Harry… What are you doing here Mycroft?

He turned around to an unexpected picture. In Mycroft's hands was an open box of freshly baked donuts. When he left it on the table by his side, Sherlock immediately noticed that he had obviously gained back the pounds he had lost -and then some- and that he was wearing what seemed to be the smallest suit he owned; the pants were impossibly tight and his belly was simply hanging out over the beltline. Sherlock's cock twitched anxiously at the sight. The shirt, however difficult the task seemed, was tucked inside the pants and covered it all. Sherlock silently cursed at that shirt.

-What is this?

-I have it all figured out, indeed. You enjoy the way my body looks when I…hm, shall we say, indulge, and I enjoy indulging. I can't help myself actually. So I concluded that we should take advantage of the situation. Do you not think so?
He grabbed one of the donuts from the table and took a large bite. Sherlock didn't hesitate for even a second. Without a word he lounged forward and took the rest from his hand. He then proceeded to feed it to Mycroft bit by bit while rubbing his soft stomach. He got rid of the shirt quick enough and appreciated the sight.

-Hm, it seems we've been 'indulging' quite a bit, haven't we?

He poked his belly with a long finger and watched it sink in Mycroft's fat. Sherlock bit his lower lip and tried to contain a joyful smile.
Mycroft looked slightly embarrassed at first but then he seemed to find his place in all that and played along. He put his hand over Sherlock's and run it over his waistline.

-You know I just can't get enough.

Mycroft's smile was positively devious. Sherlock simply grabbed another donut from the box and stated

-Oh, we'll see about that.