In a nostalgic flashback to All Might's earlier days in California, the fledgling hero finds himself entwined in a dangerous robbery at a casino, orchestrated by a band of villains. Thankfully, he receives assistance from his classmate and close friend, David Shield, who would later evolve into a prestigious scientist. They collaborate in developing many of All Might's defining suits. Transitioning to the present, All Might, together with Izuku Midoriya, warmly accepts an invitation from David's daughter, Melissa, to surprise her father on I-Island, a stunning floating city.
Upon reuniting with David, he conducts a series of examinations on All Might and makes a troubling discovery: All Might’s Quirk is perilously draining. This alarming revelation sends David into a panic as he fears the likelihood of All Might failing in his vital role as the Symbol of Peace. Simultaneously, Melissa shows Midoriya around the island, where they unexpectedly encounter a gathering of Midoriya's classmates from Class 1-A, each attending for their own individual reasons. The group partakes in exhilarating activities before Melissa invites everyone to a grand gala featuring the heroes.
Before the evening begins, Melissa shares with Midoriya her secret of being Quirkless, a shocking confession that stuns him, reminiscent of his own past when he lacked abilities. However, she soon surprises him with an incredible gift: the "Full Gauntlet" — a groundbreaking mechanical arm designed to maximize his Quirk’s potential without putting him in harm's way.
As the festivities unfold, the atmosphere shifts dramatically when Wolfram, a devious terrorist villain, stealthily seizes control of the island's security operations and presents a menacing ultimatum: he will eliminate the island's inhabitants unless his demands are satisfied. He successfully immobilizes the attending heroes, including All Might, and takes David and his aide, Samuel Abraham, hostage, planning to infiltrate the island's vault.
In the turmoil, Midoriya, Melissa, and several members of Class 1-A manage to slip away from their captors, deciding to execute a daring rescue of the hostages by climbing to the top of the building to disable the security system. However, upon detecting their escape, Wolfram retaliates by unleashing a swarm of adversaries and security bots to thwart them, forcing the group to disperse and tackle various challenges. Ultimately, Midoriya and Melissa stand united, undeterred in their mission to save the day.
As they make their way to the pinnacle of the tower, the true intentions of David and Samuel come to light. They had cleverly devised a distraction to recover their most coveted invention — a groundbreaking headset designed to amplify individual Quirks to extraordinary levels. Previously seized by their project's sponsors, this powerful device was intended for All Might, enabling him to uphold his iconic role as the symbol of peace. In a startling twist, Wolfram, initially appearing as a mere antagonist, is revealed to be a mercenary under Samuel's command, aiming to confiscate the headset for himself. Wolfram tries to eliminate Samuel and Melissa, but David and Midoriya spring into action, thwarting this treacherous plot.
Unrelenting, Wolfram kidnaps David, aiming to dispose of Samuel and Melissa. Undeterred, David and Midoriya join forces to combat him. Yet Wolfram manages to fend off Midoriya in a risky escape via helicopter. Just as despair looms, Melissa takes command of the security system, freeing the captured heroes. In a timely manner, All Might bursts onto the scene, thwarting the helicopter's escape.
In a climactic twist, Wolfram activates the Quirk Amplification Device, boosting his powers to metamorphose into an intimidating metal form, with David ensnared inside. Overwhelmingly powerful, he easily bests All Might, revealing the additional Quirk he acquired from All For One, All Might's long-standing enemy, as an attempt to break the spirit of the Symbol of Peace. As All Might grapples to match Wolfram’s upgraded capacities, Midoriya leaps into action, joining forces with his mentor to confront this formidable foe.
As the fierce battle continues, the rest of Midoriya's classmates arrive to provide their support, combining their strengths. Ultimately, All Might and Midoriya harness their One For All powers together, defeating Wolfram and rescuing David. In the aftermath of their hard-fought victory, the students celebrate, while All Might and David reflect on the promising new generation of heroes rising—Melissa and Midoriya, poised to uphold the mantle once All Might’s Quirk ultimately diminishes, securing a brighter and safer future for everyone.
