As All Might and Deku arrive on I Island, they are greeted by Melissa Shield, the daughter of the organizer of the I Expo. Melissa is a Quirkless girl, but she has inherited her father's genius for inventing support items for heroes. She shows them around the island, and they meet other prominent figures in the hero community, such as David Shield, Melissa's father and a former colleague of All Might's.
At the I Expo, they see all sorts of new gadgets and tools that heroes can use to enhance their abilities or make their jobs easier. Deku is especially excited to meet an inventor named David Shield, who has developed a suit that can amplify the user's Quirk to incredible levels. But David is estranged from his daughter, and All Might knows there is something more to their strained relationship.
As the convention gets underway, a villain named Wolfram and his henchmen infiltrate the island and take Melissa hostage, demanding that David give him a dangerous device he had been working on. Wolfram plans to use the device to create a massive explosion that will destroy the island and kill all the heroes and their families.
All Might and Deku try to confront the villain, but they are quickly overwhelmed. The only ones left to fight are the students of Class 1-A, who had arrived on the island for a class trip. They work together to overcome their fears and use their Quirks in creative ways to defeat Wolfram and save the island from destruction.
In the aftermath of the attack, All Might learns the truth about David's past and why he had been estranged from his daughter. He helps the two reconcile, and Melissa shows them her latest invention: a pair of gloves that can boost the user's Quirk without any negative side effects. All Might and Deku return home, grateful for the experience and the opportunity to inspire the next generation of heroes.