Attack On Titan 1

Humanity's numbers have been decimated, and the remaining population lives inside an immense walled city to protect them from the monstrous and mysterious titans in this bestselling manga series that marries "The Passage" and "The Walking Dead."
Several hundred years ago, humans were nearly exterminated by giants. Giants are typically several stories tall, seem to have no intelligence and who devour human beings. A small percentage of humanity survied barricading themselves in a city protected by walls even taller than the biggest of giants. Flash forward to the present and the city has not seen a giant in over 100 years - before teenager Elen and his foster sister Mikasa witness something horrific as the city walls are destroyed by a super-giant that appears from nowhere.