Shingeki no Kyojin

Humans are nearly exterminated by giant creatures called Titans. Titans are typically several stories tall, seem to have no intelligence, devour human beings and, worst of all, seem to do it for the pleasure rather than as a food source. A small percentage of humanity survived by walling themselves in a land protected by extremely high walls, even taller than the biggest of titans. Flash forward to the present, and mankind has not seen a titan in over 100 years. One day, 10 year old Eren and his childhood friend Mikasa witness something horrific as the city walls are destroyed by a colossal titan that appears out of thin air. As the smaller titans flood the city, the two kids watch in horror as Eren's mother is eaten alive. Eren vows that he will murder every single titan and take revenge for all of mankind.