Leatherhead. He had been so strong, so kind, so loyal. He had fought with and for the turtles many times, risking his life for their safety and had been a place where Michelangelo felt he could relax. He had trusted Leatherhead with his life and Leatherhead had done the same. Yet when he had to choose between his brothers and his old friend his choice had placed the crocodile in the grave. He had killed him. Michelangelo Hamato had killed Leatherhead, someone who'd trusted him with his life. Leatherhead who had been through experiences so terrible he didn't even have a name before they met. Mikey just wanted to bury Leatherhead and forget about what had happened. Pretend he was still alive, that if Mikey walked far enough down the sewers he would find him. He wanted to pretend that his friend had never been possessed by a mindworm.
But he had. It was an undeniable truth that sent splinters of agony into his heart. Every time he thought about it Mikey would almost double over with pain. The fat that it was probably what Leatherhead would've wanted made it worse. Mikey had killed a being that was willing to die for him. Mikey killed someone. He might as well say it. "Michelangelo Hamato killed someone in cold blood." As soon as the words fell from his lips he wanted to cry again, to allow himself to collapse and curl up into the tightest ball imaginable and grip his own arms way too tight. He just wanted to block everything out and allow himself to focus on the pain.
Because Leatherhead had been willing to live, fight, die and kill for Mikey. He would've given anything to ensure that the turtle and his brothers were safe from harm. Leatherhead. He died. Not of old age, not of a wound from an enemy, but with a bashed in skull from his first friend.
Mikey had thrown up. Vomit on the ground next to Leatherhead's body. Sick mixing with blood and tears. The vomit belonged to Mikey, the blood to Leatherhead and the tears to them both. Mikey had seen it. Seen it when the mindworm had been crushed and the crocodile regained his mind. Just in time to feel the agony of his broken skull and to see who had hurt him that way. And though Mikey did not know it, to mourn the passing of the innocence in his friend.
When they had buried Leatherhead Mikey hadn't even said goodbye. He had been to selfish too say goodbye. Too self-absorbed to say anything. He had merely stared off into space. Mikey was in pain. Physical pain. His chest ached and he couldn't move. His muscles were on fire, burning, aching with a horridness he didn't even know existed.
The touch of his brothers and father burned with a slow, long-lived, pain, the thought of the love he was receiving without Leatherhead like acid slowly corroding his skin and bone away. Leatherhead would have to be remembered because for him Mikey would ensure that the colour of his mask would prompt the words orange as pain.