Set during Season 2 finale
Disclaimer: if I owned this Sam and Dean would be tied up in my closet… just sayin'
Prologue
Sam's POV
Everything started on that night when I was six months old, but people seem to forget one of the most important parts. Azazel giving me his blood, while extremely import albeit disgusting, is obviously not the part I'm talking about. My mother dying over my crib, while sad and horrifying, isn't it either. Even my dad coming in to find my mother on the ceiling and staying trying to save her isn't what I'm talking about. I'm talking about the perhaps 2 minutes that happened after this: I'm talking about the decision to hand my infant self off to my toddler older brother therefore giving him a responsibity that would forever change the course of the entire world. This event was, like I said, monumental to say the least, but it was what came after it that sealed the deal(no pun intended).
The words that determined my life and sealed forever this shifting of destinies were said repeatedly, but oddly enough never to me. I always heard them growing up thinking it was a normal thing to say. I never thought they meant much, but that was before I realized what they meant. Two words said over and over again my entire life and I never understood the real meaning of them. When the truth hit me I had that odd feeling of complete stupidity, that sense of how could I have not realize? That click in your head, the imaginary light bulb, that OH! That finally realization. Honestly even with the extremely tense atmosphere I wanted to laugh, granted laugh hysterically, but laugh all the same. The two words that until that moment of realization meant nothing, but now meant exactly everything: Protect Sammy. Those two goddamn words.
They did more than just tell an older sibling to protect their younger brother. To any normal kid in any other situation it might not have changed much, but when was Dean ever normal? To Dean this was a mantra, a job, a responsiblity, but more than anything a way of life. At this point you're probably thinking why are you telling me this, or I already got this, can we move on, so now I'll explain why this had to be explained before anything else. Why this was more important than anything else: Because it caused an act that created a domino effect which forever changed this entire universe.