This is trash, don't read this. I've just had this idea in my head for a while now and...just don't read it. I might revise it later and make it actually good but for now...sorry.
Working with mutagen was a dangerous task, one wrong move and there would be nothing but chaos. While trying to create a retro-mutagen Donnie had taken all necessary precautions and then some. But accidents happened. Mutagen was a highly unstable substance; there were explosions and spills and unbalanced formulas. Despite all of this, Donnie never sustained anything more than a bad burn every now and then. None of his brothers ever came into the lab for extended amounts of time so they were never there for any of the big mishaps. Donnie was glad for this fact. If his brothers saw the burns and scars that peppered his hands they would be worried, maybe even scared. So the lab was kept restricted for most of the time and Donnie made sure to wrap his injuries before anyone could see them. However, burns and scrapes were not his biggest problem.
It was few days after Donatello had discovered the retro-mutagen and had helped turn April's father human once more when things started to go bad. One night without warning, Donnie closed off the lab; sealed it up tight in a frenzy of wielding tools and fire. That night had been particularly bad for everyone.
Mikey had been the first to hear the noise, a deep distant echo that bounced around his head. He opened his eyes slowly. He wasn't quite ready to relinquish his last few hours of sleep to the noise. After several minutes of the noise it was clear that it wasn't going away. He huffed sadly as he shed his blankets to meet the cold, night time sewer air. It came to no surprise to see Raph and Leo up when Mikey made his way to the hallway.
"What the heck is goin' on?" Raph asked, the usual venom of his voice being replaced by a suppressed yawn.
"It sounds like it's coming from Donnie's lab." Leo replied in the same sleepy tone.
The three brothers groggily made their way to the lab where they found Donnie, wielding torch in hand, sealing the large hanger doors that opened out into the subway shut. There was sweat dripping down his face and his movements were jerky and rushed. The wielding job looked like a mess, chard marks were everywhere, and even the floor was not safe from the crackling flames.
"Donnie? What are you doin'? It's one o'clock in the morning."
Donnie jumped at Raph's voice, making another stray mark on the doors. Frantically, he turned the torch off. He reached to his eyes as if to take of his usual wielding goggles but they weren't there. The same thing happened when he tried to take of his usual wielding gloves. He had forgotten to wear any safety equipment, something highly unusual for him.
"G-guys! Whatryou doing here? I wasjust, just doing some stuff. Juststuff. Somestuff." Donatello's words were choppy, running together in a frenzy. One of his eyes had a slight twitch to it.
"Have you been up all night Donnie?" Leo reached forward to his brother but Donnie jumped out of his reach.
"No. Yes. Maybe? What timesit? Did I wake you? Sorry, 'mreally sorry. Ok, I'll be quiet. You guys should 'eave now. Leave now."
Now Leo was defiantly concerned. Donnie wasn't acting like himself at all. He usually got a little wound up when he stayed up to late but there was something more going on. Donnie kept twitching and his eyes were dilated. He wasn't acting mad at them for being in his lab without permission nor was he irritated at them for disrupting his work. If anything he looked scared.
"You alright D? You look a little pale." Mikey tried to brush his hand against Donnie's forehead to see if he had a temperature. In turn Donnie smacked his hand away.
"Don't touch me! Do. Not. Touch. Me!" He screamed out.
"Gesh Don, what's your damage tonight?" Raph made a third attempt at grabbing his brother.
"I said don't touch me! Now get out! Get out, get out, get the hell out of my lab!"
That was the last thing said before Donnie roughly bushed all of them through the lab's front doors.
"What the shell just happened?" Raph asked in confusion.
Mikey and Leo exchanged hurt, questioning glances.
"I don't know. As leader I think it's best if we go back to sleep and let Donnie have some alone time. We'll talk about it later."
Later never came. By the time the brothers started morning training the lab had been completely wielded shut.
After that Donnie refused to leave his room except to eat or get water. He skipped practice which worried Master Splinter more than it angered him. Everyone tried to coax the purple banded turtle out; Mikey asked him to play board games, Raph threatened him, Leo tried to get him to play video games, April asked him if he wanted to watch some movies or hang out, and even Casey tried to rile him up enough to come out. But nothing worked.
Soon Donnie stopped coming out for food. This was especially disheartening. Everyone would take turns bringing him food and trying to talk him into coming out. Every time they would just end up putting the plate down outside his room and coming back to find that it had been barely touched. The cycle continued for several days until one day when everyone was in the living room watching cartoons and trying not to think about what was wrong with the technologically inclined turtle. They were halfway done with watching a re-run of Space Heroes when there was a soft shuffling sound. Standing by the dojo was Donnie; or at least there was no one else he could be.
His usual olive coloured skin tone had turned into a sickly pea green, everything about him seemed smaller and thinner, and his shell was bumpy and flaky. Pale scars ran down his plastron, on one side it looked like an entire piece had been picked off.
"There's something I need to tell you guys." Donnie's voice was raspy; the area around his mouth was dry as a bone despite the thin line of drool falling down his chin.
Everyone in the room was in shock over Donnie's state. April was the first to take action.
"Oh my god, Donnie what happened to you?" She ran over and helped Donnie down onto the couch beside Mikey.
Leo and Raph ran off quickly to get Master Splinter and arrived a few seconds later with their father by their sides. They still hadn't said anything, too shocked by their brother's appearance. Once Master Splinter saw his son, he rushed over to his side.
"Donatello, my son, how did this happen?" Master Splinter's eyes darted up and down his son's figure, taking in all the damage that had been done to it. There was silence in the room as everyone held their breath. Donnie let out a sharp cough before speaking.
"The mutagen, I'm sorry I should have told you all sooner. I was scared. When I figured it out I was so scared for myself and everyone else. I'm sorry, I should have told you."
"What about the mutagen Donnie? What happened?" Leo was knocked out of he shocked trance and went to wrap an arm around his brother. The action cause Donnie to flinch but he did not pull away.
"Mutagen, while not stable, is usually safe to be around as long as you don't come in direct contact with it. But it was still a chemical. I should have been smarter, I should have known but I-I didn't. I'm s-sorry. I'm s-so s-sorry."
"Hush Donatello, it is alright. Please my son, tell us what is wrong."
Donnie stared at the floor, his eyes absent and misted over with film. He didn't cough again but he did make a noise in the back of his throat.
"My tests. I tried to be careful, I did everything I should have done to contain the substance on a physical level but it wasn't enough. I didn't realize it at the time but during one of my tests something happened. I didn't realize it until now but-but some the substance turned…radioactive. The lab walls contain it but…but I spent too much time there. I started feeling weird a few days after April's dad got back so I did a test on myself. The radioactive mutagen reacted with the mutagen I have in my blood stream and now…" Donatello broke off and started coughing violently into his hand.
"That's why you closed up the lab." Raph said with sudden realization.
"Mhm." Donnie absentmindedly scratched at his plastron causing little flakes to fall onto the ground. "Shell rot." He said once he saw everyone looking at him.
"Do you think, Donnie, do you think you'll be able to cure it? Donnie?"
Donnie didn't respond to Mikey's question.