Attack On Titan 1 (Kodansha America, Inc)

Several hundred years ago, humans were nearly exterminated aby 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 aby a super-giant that appears from nowhere.