A/N: Eep! Bit by the Muse Bug again! This came to me as an off-shoot from another inspiration for a new fic. Oh boy, I'm in trouble! For those following Becoming Splinter don't worry, I do not have writer's block. I'm working on it. Just been a little busy, but this fic kept poking me so here it is!

Responsible

Why? Why couldn't you have just listened?

He couldn't understand why someone could be so foolishly stubborn even after repeated warnings. If only he had just listened and stayed home. Why had he insisted on constantly putting himself in danger?

Donnie huffed out a heavy sigh and hung his head low but his eyes never strayed from the giant canister holding the glob that was once named Timothy. Despite all the grotesque mutations he had witnessed, Timothy's was the most heartbreaking and unsettling. Once a burly young man, he had been reduced to a translucent, gelatinized creature. All of his internal organs were put on display as if he was a living anatomy lesson. Ironically, it was the most human part of him. Timothy's eyes darted around the lab and his mouth gaped open and shut like a fish. Little air bubbles escaped his lips and danced their way up to the top of the canister.

"I told you to stay home, Timothy. I told you to give up being Pulverizer. I told you to stay away from The Foot. I told you not to mess with mutagen. What were you thinking?! Why did you think mutating yourself into this was a good idea?!"

Donnie's head fell into his hands. Tears stung his eyes but he fought against releasing them. Lost in his mourning, Donnie did not notice the slender hand that had snaked its way onto his shoulder, jolting him suddenly out of his thoughts.

"My apologies. I did not mean to startle you," Splinter chuckled lightly. "Why are you still up?"

"Couldn't sleep," he stated bluntly, too emotionally spent to muster anything more. "Next time, can you be a little less…ninja. I can never hear you coming."

"Would you ask a duck to stop quacking? Ninjistu has been my entire life. I cannot change that or my nature. Much like you cannot change the events that transpired tonight."

Donnie sighed sadly. "I cannot change what happened but I still need to fix this. He got into this mess because of me. It's all my fault and I owe it to him to create a retromutagen."

Splinter quirked a quizzical eyebrow at his son.

"This is…your fault? Did you push him into the mutagen?"

Now Donnie lifted his eye-ridge in confusion.

"Well no. But we are the reason he was inspired to be a vigilante crime fighter."

"Oh I see. So you forced him to take the identity of The Pulverizer and challenge dangerous criminals."

"No," Donnie shook his head, a bit frustrated. He hated when Splinter entered into these logic games, and tonight he was just too spent for this type of conversation.

"I am confused, my son. Which part of this situation is your fault?"

Splinter pulled up a chair and sat across from Donatello. The young turtle's eyes shifted around avoiding meeting his father's gaze directly.

"You said I was responsible for him."

Splinter sat silent, recalling that day when Pulverizer had accidentally hitched a ride to their lair. Donatello had taken it upon himself to teach the foolish lad basic self-defense skills. He had called the boy a buffoon unworthy of the honor.

"You told me that as his teacher anything that happened from that point was my responsibility. And I failed him. This is all my fault, Otousan."

Otousan. Once they had entered the teen years - and earning their masks - the young ninjas had taken to calling him sensei rather than father. The familial title has been used so infrequently these days that being called father was a signal of distress – that the boys needed the emotional support that only a parent could provide.

"Donatello, do you remember that day Michelangelo convinced you boys to participate in his skateboarding stunt in the lair? You boys were creating such a ruckus that I was unable to meditate. What happened after I had caught you boys in action?"

"Mikey ran into us."

Splinter chuckled at the memory. "After that."

"You grounded us," Donnie stated pointedly unsure where this conversation was going.

"Indeed. I had grounded you - forbidden to leave the lair. What happened next?"

"We snuck out to go skateboarding."

"What had possessed you boys to defy my orders?"

A pinch of guilt fluttered in his heart at the memory. Donatello was not a rule breaker but that day he definitely was not an obedient son.

"We were bored, and Raph convinced us we could go out and sneak back before you woke up."

"Remind me again what happened after you had snuck out."

Donnie gulped as that day replayed in his mind. "The Stockman-Pod incident."

Splinter nodded. "As your father and your teacher, I am responsible for you boys. Was it my fault that Stockman picked up the T-pod and created that mechanical mayhem?"

Donnie's brow furrowed in confusion. "Of course not! That was Mikey's fault! If the numbskull hadn't dropped it, none of that would have happened!"

"However, if you boys had just followed orders, Michelangelo would never have dropped the T-pod."

Donnie tapped his chin with the knuckle of his middle finger. "Then it's Raph's fault that we left the lair. It was his idea."

"I see! So Raphael held his sai against your back and forced you to the surface."

"Well…no. I-I don't understand. I feel like this is just one riddle after another."

Not much usually escaped Donnie. He was always mocked for being the geeky science genius yet common sense and "Captain Obvious" moments tended to elude him. Or maybe he was just too exhausted. Now he was wishing he had gone to bed.

"Let me ask you this, Donatello. Leonardo is your leader, and he is responsible for your safety and well-being. He devises strategies that are in the best interest of you and your brothers. Yet, Raphael has a bad habit of defying his orders and doing his own thing. One of those times resulted in Michelangelo being injured. Was that Leonardo's fault? Should Leonardo have tried to control Raphael more?"

"That's not possible," Donnie snorted with a slight eye roll. "No one can control Raph. He's so stubborn. He never listens to anyone anyway. I've tried rationalizing with him and he just beats me up."

"So you are saying that Raphael is in complete control of his own actions?"

"Of course! Oh…"

The spark of realization flashed in Donnie's eyes. It never mattered what he did or said, Timothy was no different than Raph - stubborn, self-absorbed, and never considered any consequences for his choices.

"My son, it is my duty to teach you the skills you all need in order to protect yourselves, to make informed decisions, and to evaluate potential outcomes to your choices. While I may have wanted to keep you concealed from the outside world, I knew that was not realistic and that one day you four would to be in full control of your lives. I spent fifteen years preparing you boys for that. That was my responsibility. I cannot control the decisions you will make for yourselves. Ultimately, you are responsible for your own actions – for your choices. In regards to Timothy, you were responsible to teach him how and when to use his skills and to guide him away from harm. Your warnings unfortunately fell on deaf ears. That was not your fault. You cannot make one listen if they refuse to hear."

Donnie nodded slightly and whispered "Hai, Otousan," signifying he understood his father's words yet he could not let go of the disappointment that he could not have prevented this fate. He stood up and walked over to the tank, placing a hand on the glass. Timothy blinked at Donnie and moved his mouth but no sound came up except for the bubbling of the air escaping.

"I promise, Timothy, that I will make this right. As a scientist it is my responsibility to find a cure for this – to find a retromutagen. And when you're human again, I can only hope that you have learned from this and will choose a different path for yourself."

Returning to his desk, Donnie pulled out his notebook and began scribbling various chemical equations as he set out to solve the puzzle of retromutation. He knew it would have a long hard journey but it was on him to help Timothy and Splinter return to their human forms. This was not only conscious a choice but it was his duty as the mutagen expert to fulfill his responsibility toward his friend, his family, and all of humanity.