A few days after Kagato is defeated everything returns to normal. Ryouko finds Mihoshi and Sasami reading shoujo manga, which Sasami mistakes as guides on how to win a boy's heart... Earth style. So Ryouko decides to try out the ideas from the manga to win over Tenchi. But Aeka finds out what her rival Ryouko is doing and tries to take advantage of the same method. Naturally, the results are less than satisfactory for all involved...

A mysterious group called Humarize strongly believes in the Quirk Singularity Doomsday theory which states that when quirks get mixed further in with future generations, that power will bring forth the end of humanity. In order to save everyone, the Pro-Heroes around the world ask UA Academy heroes-in-training to assist them and form a world-class selected hero team. It’s up to the heroes to save the world and the future of heroes in what is the most dangerous crisis to take place yet in My Hero Academia.

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.

In a society devastated by the effects of an all-out war between heroes and villains, a mysterious giant fortress suddenly appears, engulfing towns and people one after another. Then, a man reminiscent of All Might, the 'symbol of peace', stands in front of Izuku and his friends...