Yes, it has been fifteen years, but Mikey was never one to follow directions. He might have grown older, but Michelangelo refused to grow up. His humor was more refined, less childish, but it was annoying humor none the less. He had learned how to balance his life, focusing in battle, and relaxing when he was not. His skills as a warrior had surpassed his brother by far, yet he was still the child. The baby that they all knew and loved. When he had been young, Michelangelo had been in constant need of rescue by his brothers, and now he was the one doing the rescuing. He didn't boast about it either, just took the thanks and let the ordeal slip from his shoulders. No one ever thought of it, and Mikey knew as long as he didn't bring it into the light, his innocence would remain in their eyes.
Fifteen years could not change Donatello's work method. He still tirelessly worked, slaving over the inventions his brothers all enjoyed. The little gadgets and gizmos he cooked up on a regular basis to sustain his brothers ever growing hunger for a stress relief. His work method did not change, but he did. He had become obsessed with pleasing those around him. Their approval was something he felt he would die without. With his little creations, Donatello became more and more sure that he could stop death. That he could prevent all of their demises, preserving the love they all shared. He was a man obsessed. His brothers seemed not to care though, as long as he kept giving them new trinkets to play with. Donatello feared the day they realized he had lost the only thing they needed him for, his mind.
When he had been young, Raphael had been a hot head. An angry ball of fire that could take his opponents down without a problem. He still could of course even after 15 years , and did so at his leisure. He roamed the streets for punks to take down, something they had once called noble. The sickening truth that Raph held would make his brothers hate him, see him for who he really was. A monster, but he had grown fond of the feeling of bones snapping beneath his fist. He hated how his mind worked, the rage had finally consumed him. The quarrels he had once had with Leo were gone. They had evaporated like the last ounce of self control he had. Raphael felt himself a vigilante now, no longer the righteous hero his brothers had once made him out to be. He was no better then the Shredder, but Raphael no longer cared. He might have hated what he had become, but the sheer power he commanded hid the pain well.
Leonardo had grown tired. He had spent fifteen years trying to keep his brothers together. Fifteen years of watching each of them plunge into a pit of madness and despair. His once soft brown eyes were now cold, harboring hate for his brothers. They had done this to him, forced him to be there pathetic leader. The face that stared at him in the mirrors reminded him that he was old now, but with age came wisdom. Vengeful wisdom. A burning need to cut himself free of these fools and go his own separate way. He only stayed to make sure Raph didn't go off on a murderous spree of joy, that Don stayed sane enough to be a coherent being, and Mikey kept himself out of harms way. Raph couldn't hide the pure animistic rage that burned in his amber eyes, Don couldn't keep the fact that he was slowly losing his mind, and if Mikey was hiding something he hid it well. Leo couldn't help but smile inside, he always did.
This was a dark little one shot I did. I just had a random thought about what will they be like in 15 years? Welp, from the darkest place of my imagination, here it is.