The movie takes place after the events of season 4 of the My Hero Academia anime. Class 1-A goes to Nabu Island for a two-month long hero internship, led by their homeroom teacher, Shota Aizawa (also known as Eraser Head). It is a peaceful and remote island where they are tasked with doing normal hero work and helping out the island's residents.
However, their vacation turns into a nightmare when they are attacked by a powerful villain named Nine, who has the ability to steal other people's Quirks. Nine is a former test subject of Doctor Kyudai Garaki, who has ties to Shigaraki and the League of Villains. He is seeking to gain more power by stealing Quirks, and he targets Class 1-A as a potential source.
All Might is not present to help them as he has retired from hero work due to the injuries sustained during his final battle against All For One. The students are left to fight for themselves and protect the island's residents, who are in danger from Nine's rampage.
Deku and his classmates must work together and use all their training and knowledge to stop Nine and protect the island. With the help of a mysterious girl named Eri, who has the ability to rewind time, they are able to fight back and save the day. The movie ends with a touching moment between Deku and All Might, as the former passes on his hero will to the latter.
