Warning: Spoilers for My Hero Academia: You’re Next Up!My Hero Academia: You’re Next chronicles the battle against a mysterious All Might impersonator who appears to have All Might-level power but intends to take over Japan as his new “Symbol”. This man, who calls himself the Dark Might after speaking with the real All Might, must be stopped before Japan is destroyed even worse than it already is.
Dark Force appears and reveals his quirk, Alchemy, which is enhanced by the quirk of another woman he is holding captive, Anna Scervino. An advanced version of Alchemy is able to take over most of the city and turn it into a floating fortress, which Dark Might uses to attack UA, where All Might is located. The students of Class 1-A are trapped in this transforming fortress, and since they are the only ones inside the fortress, it is up to them to figure out what is happening and put an end to the Dark Might.
Dark Might’s final battle spirals out of control
Dark power becomes monstrous as Anna loses control
Deku teams up with a boy named Julio, who was once Anna’s servant and calmed her quirk, and desperately tries to free her from the suffering that the Dark Power is causing her. Julio can no longer use his quirk due to injury, and has several prosthetics, including an arm, leg, and eye. He and Deku fight against the Dark Force, which continues to use Anna’s power to enhance its own. Dark Might is able to land his own blows and even withstands Deku’s strongest attack, and the battle proves difficult even when Bakugou and Todoroki show up to offer help.
When the Pro Heroes begin attacking the fortress from outside, Anna’s power begins to spiral out of control, just as Giulio warned earlier in the film. Believing that this will grant Dark Might unlimited power, Dark Might leaves the fortress and transforms into a new monstrous form, increasing his power far beyond that of a Quirk user.. Anna’s power begins to cause thorny vines to grow around her, lifting her high into the air and forcing Julio to climb upward in an attempt to help her regain control. However, Julio is still unable to use his quirk.
Connected
Julio ends up coming into direct contact with Anna, instead becoming the target of her quirk. Although risky, it becomes apparent that Anna’s quirk is compatible with Julio and increases the power of his quirk enough that he can use it again. Julio uses his Neutralization Quirk to silence her, seemingly forever, and eliminates the source of the Dark Might’s immense power. The monstrous form of the Dark Might succumbs and he is defeated.
Now that Anna is effectively quirkless, she can lead a normal life, signaling the end of her contract with Julio. However, Anna has fallen in love with Giulio and asks him to stay with her no matter what, to which he agrees. Dark Might has been taken into custody and will no longer pose a threat to anyone. The heroes managed to save YA, and many episodes show characters like Deku and Bakugou’s mothers rejoicing at stopping the fortress. That’s almost all you need to know about how My Hero Academia: You’re Next ends.