Chapter Text
The first time that John Winchester noticed that something was going on with his sons, was when he found them interchanging the smoke from joint a from mouth to mouth. Both of them naked, and sharing the bathtub, clearly too narrow for two guys their size. He did a double take and just stopped there, mouth gaping, staring at them without realizing at first what was going on. First of all, why were they bathing together? And more importantly, was that a tongue he just saw? He excused himself for the intrusion and just ran off the motel, searching for the nearest bar.
The second time he saw them, was when he heard shouting from the parking lot, and when he came to the window to find out what was going on, he saw Dean pushing Sam against the door of the Impala and just pinning him there, to then start kissing him fiercely. Was Sam moaning? Out there in the open? Where the fuck was the whisky?
The first time he caught them actually having sex, he was drunk enough to find it amusing instead of feeling angry. But he was also lucid enough to walk away as soon as he noticed that his cock was growing inside of his pants. He had a boner. From watching his oldest son sucking his youngest while Sammy screamed like a bitch in heat. And was that a tail he was seeing? Fuck. But he still didn't walk away from the room until he made sure that Dean had fed Sam his cock properly.
By the fifth time he caught his sons screwing each other, he was completely aware that they both had noticed his interest in their mating sessions, and seemed to be more than fine with letting him watch. He learned soon, though, that he shouldn't get closer to them or Dean would start growling at him, a strange glow in his feline eyes (Wait, did he say feline?). So he simply sat on the opposite couch and let them fuck without saying anything, while he stripped his own cock hard an fast, shame and guilt be damned.
By the time he actually knew what he was dealing with, it was already too late. A large creature, similar to a cougar but way bigger to be a normal one, was fucking Sammy like its life depended on it, and his youngest was just lying there, mewling, his little cock leaking into the carpet and his small body shaking with the violent thrusts of the creature that he realized, when green eyes looked at him angrily, was Dean. At the base of Sam's tailbone, was a very real tail, and his ears started growing at the sides of his head. The transformation was still incomplete, but if what he had read was true, it was unstoppable. By the time the Deity was done, both Sam and Dean would have turned into shifters, into cougars.
Three months later, Sammy gave birth to his first litter, as a cougar, while a smiling Dean watched over him, looking smug, with his fangs showing.