Notes:

Peter Laird and Kevin Eastman pretty much said that the Turtles from oldest to youngest: Leo, Don, Raph, and Mikey. And considering both Leo and Splinter assume Don to take care of everyone, I guess that clinches Don as the second eldest.

My first TMNT fic with my fave Turtle.

Oniisan

Donnie sighed as he removed his goggles from his forehead to wipe the lens with a piece of white cloth. His distracted gaze fell on his table overcrowding with electric wires, broken computer parts and various books, magazines and manuals that for some reason he couldn't find the time to sort it away in his bookshelf. Even his screwdrivers and half-filled beakers were carelessly shoved to the side along with his mathematical notes and half-finished inventions, seeing these things now, so late in the night, completely abandoned and forgotten, Donnie found himself frowning in self-reproach. It wasn't like him to be so disorganized. He should at least find the time to clear his desk.

Except he couldn't make time, he corrected himself with a wince. Ever since getting his IT tech support job, he can barely squeeze in time between practicing his ninjutsu, tinkering with his machinery, fixing things, resuming night time patrol and even as mundane as hanging out with his brothers.

His brothers. Donnie resisted the urge to groan out loud in annoyance. Ever since Leo left, things had been getting a little weird... Raph would go out without saying a word, without telling anyone where he's going. He'd return early in the morning, and spend the day away sleeping, missing out their daytime activities.

At first Don let it slide; it wasn't really the first time Raph would run the patrols on his own. And seeing how he and Leo didn't really parted ways on good terms, he figured his little brother needed ample time to lose his steam.

Leo and Raph's bickering were as old and constant as... well... breathing... growing up. Don could only watch in amusement and worry as these two would literally get into each others' shells, from serious discussions on how they should attack their enemies to banal issues like what kind of show they're going to watch in TV. He couldn't figure out why they argue so much, but somehow that never did escalate into anything violent. Whenever Leo or Raph DO fight over something violent, he and Mikey make it a point to scoot away from ground zero and munch pork grinds, or pizza, or anything just to keep them busy until one of them stalks away fuming.

But after Leo left for his training mission, Raph's energy seemed to have gone with him, not even Mikey's renewed mission of cheering him up seemed to bring him to his good mood. He became more tired... irritated and snappish.

It somehow became worse a few days ago, when the three brothers were eating breakfast. A rare moment for all of them.

"Donnie, have you seen the news?" Mikey said in obvious excitement. Raph was playing with his bowl of cereal in disinterest.

Don yawned, pouring himself a second mug of coffee. Leo made many vocal warnings that too much caffeine intake was unhealthy... but Donnie blissfully made those warnings banish from his mind by making a mental note that the toaster isn't working properly, he'd have to find the time to fix it later that afternoon, and that he should read the manuals April gave him as reference material for his job... which would start around nine.

Come to think of it, Don realized that he hasn't been watching TV lately. "No, what?" he asked.

Mikey began regaling about this vigilante the media began calling as "The Nightwatcher", at first Donnie thought it was Mikey letting his obsession with his Batman comics getting the better of him, but when his youngest brother began to show newspaper clippings of the Nightwatcher sightings, Don felt his eyebrows draw together in grim disapproval as he read how the vigilante captured those people by tying them to a chain and left them hanging in the air, scared out of their wits.

And before Donatello could stop himself he blurted out matter-of-factly. "He's nothing but a violent brute, Mikey."

Mikey looked like Donnie just punched him in the face, and Raph looked upset by his declaration before he masked it with a look of annoyance. "What's wrong with him?" Raph demanded.

Don looked at his brothers as though they've completely lost it. "Some nut head's going around terrorizing people in the neighborhood. That's what's wrong."

"Aw, bro, they're the bad guys he's terrorizing," Mikey said, feeling the need to defend the guy from such an unfair proclamation, "That's pretty cool."

"No it's not." Don said, raising his voice, standing up, coffee mug in hand. "That's just an attention wanting bully who feels using force to intimidate others."

Raph gave a derisive laugh, surprising the other two. "Man, for a moment there you sound like Leo." He shoves his chair away from the table and left, his cereal bowl forgotten. Mikey quietly took his clippings and placed them in the safety of his box, pouting in disappointment. He quickly followed Raph's lead.

Don sat on the chair, his mind reeling in shock by what just happened. It wasn't like him to act so self-righteously... he was the sort of person who'd take stock the situation and weigh in the pros and the cons before he can honestly give his opinion. But seeing the look of misplaced happiness on Mikey's face over this masked man's activities made him react with an unusual protectiveness.

He wondered if this was what Leo felt when he deals this sort of thing... and for that brief moment, he felt sorry that his eldest brother wasn't here to back him up that he was right.

Because Mikey couldn't talk to him for a couple of days, offended for the Nightwatcher's sake. But the youngest brother wasn't known for holding out grudges for long and soon began joking and talking with Donnie again as though that scene never happened.

Raph became more withdrawn from him after that day... in fact he made it a point to avoid him altogether and somehow managed to bring out a temper that Don never knew he had it in him. The two of them started fighting over the phone and in their home... Don demanding what Raph is doing to himself and Raph telling him to mind his own life and stop acting like Leo. Mikey could only watch in mortification as the three of them were slowly starting to fall apart, that even April and Casey can pick up the tension.

His home has become like an empty shell. Each of your brothers has strengths and weaknesses; you must be strong when they are weak. Master Splinter gently reprimanded him when a disgruntled Don watch Raph leave after their fight, wishing that it was the latter Splinter sent away instead.

Don stared at his goggles as he cleaned it with his white cloth quietly, no longer in the mood to fix things today as their father left them to their devices. He can tell that Splinter's lack of action was his hope for Raph to tell him what was bothering him... but Don couldn't help but be worried for his little brother, another thing that was eating up his time. And he was frustrated by the knowledge that he was powerless to help him.

He can fix any equipment, can memorize and quote literary works smoothly and heck, does medicine in a daily basis... but when it comes of being the big brother. Don felt a sinking sensation that he was failing miserably.

Everyday, Don wished Leo comes back soon and take this mantle away from him.

He just wasn't strong enough.