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 city protected by extremely high walls, even taller than the biggest of titans. Flash forward to the present and the city has not seen a titan in over 100 years. Teenage boy Eren and his foster sister 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 their mother is eaten alive. Eren vows that he will murder every single titan and take revenge for all of mankind.
I'm not an expert of anime. I haven't even read the manga, which I'll do it btw. But I can assure you that attack on titan will keep you interested from the very beginning thanks to a gripping and original plot. There isn't a single boring episode, it's always suspance and action. It may seem a superficial fantasy anime but it actually deals with important topics, such as freedom. Furthermore, the soundtracks are so good that you will start feeling patriotism for an imaginary country.