The Last of Us is a game known for its powerful story, its atmosphere, its ease in controls, and its all around solid gameplay. The game doesn't wait for you to be prepared for what's about to happen, it waits until you're having the time of your life and then jumps out from behind a corner and breaks your shins with a wrench, then waits as you're just done taping them up as best you can, only to break your femurs. If the story isn't enough to get you in emotional crutches, there's enough laying around from other people to have you questioning humanity. Here's a list of the most gut-wrenching non-story moments to get you going.
In chapter five, Joel and Ellie enter an overgrown and slightly flooded hotel in Pittsburgh. If the player goes room to room, you find a message written on a wall by, assumedly, a civilian to someone who might be his wife. The message warns Sara that the area it isn't safe but that line is scribbled out and replaced with, in a different font and color, "don't worry we take good care of her..".
The worrisome part, and probably the more disgusting part, is that the hotel is overrun with bandits and raiders. At this point, we've seen what horrors that the bandits and raiders are capable of. The game has conditioned us to be more scared of fellow humans than the victims of infection. The messages quiet appearance only drives the eeriness. It only appears in that one spot, is possible to miss, and is never mentioned again. The woman, and possibly Dexter and Neville, are just a few more victims in the fall of humanity.
As we recover from the emotional train wreck / rollercoaster that was chapter nine, chapter ten starts off mercifully uneventfully. Relatively. The game still doesn't take it easy on you. Ellie and Joel are walking through a highway stuffed with abandoned vehicles just before another deserted quarantine zone. At some point on the highway, we come across a camper-van with a photograph inside.
When you investigate the photograph, you find that the other side of it says "forgive us". Alone, this probably isn't the saddest thing to ever occur in this game, but once you look around, it hits you. At the back of the camper, you find the bodies of an adult and two children. At the door almost falling out of the vehicle is the body of another adult. Now, putting that together with the message left on the note leaves a few theories about what happened.
One theory is that the father killed the family so that they didn't have to suffer through the outbreak. A baseball bat is found towards the back of the camper where the three bodies are. This could mean that the father killed them with it, the only weapon found in the area, and then gave himself up to the infected since you find a male body at the door.
Another theory, and probably the more logical one, is that someone killed the father at the door and then killed the rest of the family. The guilt gets to the murderers so they write "forgive us" on the back of the photograph, and cover the bodies up.
Either way, this bright happy family in a photograph met a grisly, tragic end - and it wasn't even the monsters who brought it.
There isn't much known about Captain Mastros, as you really only find two notes where his name is mentioned. It's safe to assume that he was a captain in the military for the Pittsburgh Quarantine Zone at the start of the outbreak. He writes, on government stationery, that the past 14 months have been a "bloodbath," that he's lost too many men and about the lose the zone. He asks for orders from a superior officer, but states that if they stay any longer, they'd all get "lynched". Unfortunately, Captain Mastros knew what was coming for him and his men.
In the only other note to mention Mastros, a team member scribbles in a notepad about how he saw his team, along with Captain Mastros, get doused in gasoline and set ablaze. The writer of the note, an unnamed soldier, states that the mob cheered and one man complained about the waste of gasoline. Humanity has degraded so far that the waste of resources is more sickening than watching fellow humans burn alive. The writer ends by saying that they were going to hunt each person in the mob down and kill them for their inhumanity.