A really long time ago, (hundreds of years ago) there lived a carefree village with carefree citizens. Some of them ran shops, some of them were farmers, and some of them were chimney sweeps and door to door salesmen and lots of other things. They lived in a little town whose name has been lost to the ages.
But the important thing about the town was that it was inside of the first wall, because the world was populated by titans! Titans are the morally ambiguous creatures that eat humans for fun and they live all over the place and they are awful, so the only places where little towns like this could be safe was inside the walls. I wonder if the walls as a whole have names or are they just called Walls or something? Anyway, the town was cute and carefree and nestled safe inside of the wall the way a penguin egg is nestled safely on a father penguin's feet and crotch-flap.
There were three walls, each with their own name and varying levels of security. Why am I repeating this is you have already watched the show? You should know this by now. Anyway, the cute little town was busy with hustle and bustle and being cute. A bread maker waved his baked wares in the face of an uninterested passerby. A precocious child stopped to pick up a shiny coin they found on the sidewalk. A typically gloomy teenager lounged in a lemon tree, reading a book on something or other. A woman disinterestedly plucked another grey hair from her head as she hoped that her husband hadn't noticed during breakfast that morning. The wall guards were busy getting crunk, as wall guards tend to do. (Some things never change.)
Suddenly, a shadow was cast over the cute little town!
IT WAS A REALLY BIG TITAN! Dare I say it, a colossal titan! It was HUGE! It was staring at the town over the wall! It had really bad teeth and a lazy eye and it looked like it wanted to eat them!
Panic engulfed the town, and the townspeople scattered like a flock of birds scatters when some jerk throws a rock to try and hit two birds with one stone and they think they stand the best chance of accomplishing this by chucking a rock into a flock of birds. The birds were crows. There was one casualty, via rock. The rock thrower did not accomplish their goal and the birds got together later to mourn their stoned comrade. It was like that.
But instead of it being a single rock, it was a big titan, and they invited all of their little titan buddies for a human buffet! Since this colossal titan wasn't strong enough to break the wall, he (I'm assuming it's a he but you can't be too sure) started grabbing the smaller titans and throwing them over the wall. It was raining titans! Since they were titans they didn't get hurt, and when they recovered from the fall they lumbered around stuffing humans into their mouths and eating them. It was CHAOS!
Soon, the titans were full and go bored, so they wandered off to another place to do whatever it is that titans do in their spare time. The town was in ruins. Buildings were pushed over, giant footsteps had trampled the flowerbeds, and someone had chewed the roof of the church off. Everyone was dead, except for the boy who was reading in the lemon tree.
In shock, he closed his book on quantum mechanics and surveyed the destruction of his hometown. The titans had ignored him in the lemon tree because lemons are sour, and titans will not eat lemons. The boy picked a lemon and squeezed it really hard, pretending it was a titan's stupid head. Lemon juice ran down his arm and got into one of his hangnails, making it sting like hell but it increased his resolve even further.
The boy's name was Cave Johnson, and at that moment he swore to invent something that would aid in the war against the titans!