Truly, the Last

Twenty years ago, a strain of cordyceps fungi manifested in North America. It began submerging itself into the bodies of human beings and ate away their brains, turning humans into zombie-like creatures that they call "The Infected".
Joel, a smuggler in his late forties, alongside his partner, Tess, were assigned to smuggle a foul-mouthed fourteen year old girl named Ellie, who presumably had the genetics to become immune to this virus, in exchange for a load of guns. Throughout the series of their adventures, Joel, Tess, and Ellie narrowed down to Joel and Ellie, and after learning that she has to trade her life and genes in to create the antivirus, Joel's emotional attachment to Ellie spiraled into an act of "all for nothing". He killed the majority of the hospital they resided in and saved Ellie right before she went into surgery. The catch is, Ellie isn't aware of any of this. She was under anesthetics while it all played out. So far, all she knows is that "They've stopped looking for a cure, I swear."
Six months have gone by and Joel and Ellie stay in Jackson County, Wyoming, with Joel's brother, Tommy, and his wife, Maria. During these six months, Ellie has become more dismissive: she curses less, pays less attention to her surroundings, and doesn't smile for days. Joel senses something is wrong. It has always been wrong. He just chose to ignore it until this day.