It is difficult to imagine what mankind was like more than a hundred years ago. The history books say that mankind lived across the world, that there were these things called 'countries, and that wars were fought between these 'countries' over things not even worth fighting for.
But a hundred years ago, mankind learned that other 'countries' were not the only enemy; mankind learned that there is more than one kind of enemy. A hundred years ago, mankind met the Titans. The history books don't say exactly what happened on that day, only that the Titans, ranging from 3 metres to 20 metres, suddenly appeared out of nowhere and attacked mankind.
Mankind responded by building the Three Great Walls, Wall Maria, Wall Rose and Wall Sina, and hiding behind them. The history books don't say how these 50 metre walls were built, but no-one questions mankind's saviors.
Three armies were also created: the Military Police, who protected the city within Wall Sina; the Stationary Guard, who protect and repair Wall Maria; and the Scouting Legion, brave soldiers who go out beyond Wall Maria to fight the Titans in their own territory.
Mankind thought they were safe, protected by the army and the Great Walls; the Titans just a myth to them. That is, until 5 years ago, when mankind learned yet again that there is more than one kind of enemy. A 60-metre Titan appeared outside the wall, its whole head above the wall, and kicked through the gate. Wall Maria fell and mankind was forced to retreat behind Wall Rose.
The Colossal Titan disappeared without a trace and, for the rest of mankind, the Titans became a myth again. But for me, that day sparked my hatred of the Titans; my village had been the first to be attacked by the Titans. I had always wanted to join the Scouting Legion, to go out beyond the wall and see the world mankind used to live in. That day, I made my decision to do so.
My commanding officer, leader of the Scouting Legion, once asked me, "Who do you think the enemy is?"
It was after two Titans, which we had managed to capture alive in order to discover their weakness, were killed. By someone using army regulation weaponry. For me, the only answer to that question had always been the Titans.
But now, as I stand atop Wall Sina, I finally understand what he meant. Just moments ago, five Titans had appeared within Wall Sina. Titans which, not more than two minutes ago, had been my fellow comrades in the army.
I had watched as people I thought I knew had transformed themselves into Titans. Traitors? No, I don't think they were ever on the side of humanity. But once again, mankind learned the folly of believing there is only one enemy. There is always more than one kind of enemy.