When he was younger, much younger, Donnie thought Raph was invincible.

He thought a lot of things were invincible. Master Spinter. Leo. His remote control car he built by hand. It was a blanket of innocence that kept his thoughts safe throughout his childhood. Master Spinter would always make it home after looking for food because he couldn't be hurt. Leo would recover from his cold because he couldn't get sicker. Raph wouldn't injure himself during his tantrums because that wasn't an option.

This façade got peeled away in degrees for Don. He was a turtle of science. He knew what it meant when you had evidence to contradict your theory; your theory was rubbish. And soon enough, contradictory evidence started piling up. First, Master Splinter had been thrown into deep waters to what his sons assumed was his demise. Then Leo had lied in a tub for months on end teetering between life and death. Both of those incidents had thrown his worldview off its axis, turning the world sideways. But Raph, Raph had been fine. Raph had never faltered. Raph had remained invincible. Until-

Don looked at the burning building in front of him, mouth far too dry from screaming, and began to realize that his theory was totally shit. Because Raph had been in there. Raph had pushed him out the front door before the building could blow. And Raph wasn't fireproof.

Mikey and Leo weren't there, weren't even within five miles when Raph rushed into the building with Don one his toes. They were across the city, fighting Foot while Raph and Don dealt with the Krang. And dealt they had. No Krang were coming out of that building after that explosion. Or any turtles.

Don tried to take deep breaths, trying to breath around the panic. He needed to look at this logically or he'd crumble. Here was his theory: Raphel was invincible. Hypothesis: If Raph was invincible, he'd walk right out of that building, just fine. Don looked up. He could see flames lick at the entryway to the warehouse, consuming the wooden beams with hot tongues. There was smoke and debris and some Krang tech that Donnie honestly couldn't care about right now. But there was no Raph.

Hypothesis: If Raph was invincible he'd walk right out of that building. Evidence proved the hypothesis false. Thus, his theory had to be revised. Raph wasn't invincible. Which mean, logically, that Raph was-

"No, no, no, no." It all came out in a stream of words. Don didn't realize he was speaking until he was on the 5th no. He wasn't going to do this. He couldn't do this. Screw the evidence. Screw the scientific method. This was a result he wasn't going to accept. Don struggled to his feet, trying to regain his balance. The explosion had thrown him against the alley wall and as a result, it was hard to stand up straight.

Or maybe, he considered, that was just his world disintegrating under his feet.

He stumbled towards the warehouse. The fire was still raging on, consuming the wooden beams of the structure. The thing was likely minutes from collapse. Don could work with minutes. He shook his head, trying to make the world stand still and stepped into the doorway only to get wretched away from the building with one strong pull.

He tried to fight at first. He had a brother to save. But then he noticed the wrapped hands, and the kneepads and the tails of a red mask blowing in his peripheral vision.

"Donnie! What were you thinking!" Raph, oh God it was really him, appeared in front of him, and shook his shoulders. Hard enough for Don to know that this was real. His brother's voice was almost gone, stolen away from all the smoke. "That place is about to collapse!"

"I…..I-" Don couldn't fine the words. How was he supposed to say something he couldn't even bare to think of? So he settled on something else. "You're okay."

Raph looked puzzled. "Of course I am. I got out the widow before the place blew." His eyes grew widened he took in the fear on Don's face. Terror he'd rarely seen present in his younger brother. "Wait, did you think?"

Don could only nod. Soon enough Raph had him wrapped up in a hug, a tight one, and Don hugged him back with all the strength he had left in his body. Mikey and Leo would find them like that ten minutes later, hanging on for dear life. Later, when they were in the lair and breathing from oxygen masks, they wouldn't speak of this. It'd remain a scary memory of what could have been. But for now, as the building burned behind them, the universe fell back into place.

Theory: Raphael was invincible. The evidence checked out. And while Don knew it wouldn't always, for now, he was content to let it be for now.