Three high school students are transported to a fantasy world. But while two are heroes, one can only be a healer.

Several hundred years ago, humans were nearly exterminated by 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 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.

While putting their hero skills to use on the peaceful island of Nabu, the Class 1-A kids face a sudden attack from a formidable villain known as Nine.

All Might and Deku accept an invitation to go abroad to a floating and mobile manmade city, called 'I Island', where they research quirks as well as hero supplemental items at the special 'I Expo' convention that is currently being held on the island. During that time, suddenly, despite an iron wall of security surrounding the island, the system is breached by a villain, and the only ones able to stop him are the students of Class 1-A.

A half human, half Yoma monster sets out to attain justice against the evil full-breed Yomas, hideous fiends who feed ruthlessly on humanity.