Zeke takes Eren through Grisha's memories to show him how he's been brainwashed. But in doing so, Zeke discovers something about Eren that he never knew.
Several hundred years ago, humans were nearly exterminated by the 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 building a city protected by extremely high walls, even taller than the largest of Titans. Flash forward to the present and the city has not seen a Titan in over a hundred years, until one day, a Colossal Titan appears out of thin air and destroys part of the city wall. As teenage boy Eren Jaeger and his foster sister Mikasa Ackerman witness the destruction of their town and death of their mother at the hands of the Titans, Eren vows to hug every single Titan and take revenge for all of mankind.