Rube: You know what happens if you keep a soul around after it's time?
George: No.
Rube: Same thing that happens to milk, spoils, goes bad. Souls go bad in all kinds of ways.
Pilot Episode, Dead Like Me
Spoiled
Dean Winchester was supposed to die after being electrocuted. He wasn't supposed to be healed by Roy LaGrange. Death had been forced to give him a second chance. Then Death cam for Dean again, while Roy healed Layla, on the day when Dean was supposed to die in the first place. Dean Winchester beat death then too. But souls aren't supposed to stay in their bodies after the day there are meant to die, they are meant to move on to whatever comes after this. Souls can go bad if they stay too long; souls can die and leave the empty shell of a person behind.
Sam watched as his brother change. It took a while actually, and there were always parts of him left. Before the incident, Dean cared about people and he cared about getting everyone out of a hunt alive. Afterwards, he was different; he'd kill and not even care about it. He willingly killed Meg without a second thought, although he claimed to be setting her free from the demon inside her. Dean had shot the guy that was attacking Sam in the alleyway the next day and didn't even blink, didn't even care. Sam had seen Dean decapitate a vampire with an evil smile on his face. And those things were only the beginning of his madness.
"Killin' that guy, killin' Meg—I didn't hesitate. I didn't even flinch. For you or Dad, the things I'm willin' to do or kill, it just….it scares me sometimes."
Dean had sensed it in the beginning. He'd known that there was something off with him. He'd hoped that it was just his way of protecting his family, that because they were in such danger he went to extreme measures to keep them safe. That was, until he started enjoying the kill. Until he started purposely hunting down things that he could beat up or exorcise or kill, just for the fun of it. A small part of him always knew that what he was doing was wrong, that it wasn't really who he was. He had become reckless, he was savage, in his own eyes, Dean had become one of the things that they hunted. He'd become evil. So with what little humanity he had left in him he fought against the darkness in him, he went to Sam and begged for Sam to kill him. Silver bullet to the heart, chop off his head, salt and burn him for all he cared. Anything to stop him, to stop what he had become.
With tears in his eyes Sam, always loyal to his brother complied with Dean's wishes. Sam knew what Dean had become and knew that it was his job to stop Dean; he had already let it go on long enough. Sam aimed the pistol straight at Dean's heart, who knelt before him in the open field with tears in his eyes. To Sam, time went almost in slow motion as Sam fired the sliver bullet and it collided with Dean's chest. Dean fell backwards onto the grass and with his last breath he gasped out: Thank you.
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