The League of Villains are chased by a cadre of Heroes while a truck carries a life-support capsule. Endeavor, Endeavor arrives and destroys the vehicle, and the villains are revealed to be clones born from Twice as the truck crashes. The figure inside the capsule, a villain named Nine, escapes amid the wreck and reunites with his team to pursue a dream of a world ruled by those with strong Quirks. Nine possesses a copy of All For One’s Quirk, granting him access to eight additional Quirks beyond his own Weather Manipulation, but he also needs a special Cell Activation Quirk to cure a terminal disease that worsened as a side effect of his modification. Daruma Ujiko’s experiments loom in the background as the plan moves forward.
U.A. High’s Class 1-A has been sent to the remote Nabu Island as part of a safety work program. Izuku Midoriya, Daiki Yamashita the current wielder of One For All, meets Mahoro Shimano and her younger brother Katsuma, who live on the island. Despite some initial hostility from Mahoro, Izuku bonds with them alongside his rival, Katsuki Bakugo, and learns that Katsuma dreams of becoming a hero while Mahoro worries about his safety. The situation on the island tightens when Mahoro and Katsuma’s father is attacked by Nine’s group and his Quirk is taken, a twist that hints at a race to identify which child might harbor the necessary Quirk, since the Quirk’s compatibility with the father’s blood type becomes a crucial clue.
Nine’s gang arrives and cuts off all means of escape, trapping the islanders and forcing Class 1-A to split up and protect everyone. Nine tracks down the children and confirms that Katsuma possesses the Quirk he seeks, prompting Izuku to intervene. Nine overwhelms Izuku with a flood of Quirks, even with Bakugo’s help, and the two are pushed to their limits. The villains are defeated only after Nine overuses his abilities and must retreat, giving 1-A a chance to rescue Izuku, Bakugo, and the Shimanos. After regrouping, the students deduce why Nine wants Katsuma, noticing that Katsuma’s Quirk has the healing power Nine needs to counter his own illness, especially when Izuku and Bakugo are briefly healed by Katsuma’s Quirk.
With renewed resolve, Class 1-A evacuates the islanders to a nearby refuge and works to separate Nine from his gang, defeating each member in turn. Nine, however, disables the remaining students once more by consuming Quirk-enhancing fluids, threatening to destroy the island. Faced with no other option, Izuku transfers One For All to Bakugo, while he uses the remaining embers to cooperate in the fight. The two finally defeat Nine, and All Might’s reinforcements arrive to recover Bakugo and Izuku, while it becomes clear that One For All still resides in Izuku — the transfer to Bakugo having been interrupted. The elder hero theorizes that the previous wielders of One For All would want Izuku to keep it.
Meanwhile, Tomura Shigaraki, Koki Uchiyama, discovers and kills the weakened Nine out of spite, underscoring the ruthless power struggle shaping the landscape of heroes and villains. With Nine’s gang captured, the island’s damage is repaired and the students head home. Izuku and Bakugo, who had briefly forgotten that one for all had been in their possession, bid farewell to Katsuma and Mahoro, with Izuku assuring Katsuma that he can become a hero just as All Might showed him it could be done.
