Nine, Slice, Chimera and Mummy attacked Nabu Island with the intention of stealing the Cell Activation Quirk from Katsuma Shimano, causing their confrontation against the students of class 1-A. Despite their numerical inferiority, they caused great damage to the island and injured many students. Nine himself defeated Izuku and Katsuki, but had to withdraw from the battle due to the pain caused by his disease in the cells.
For their part, the students also withdraw to attend to the wounded and provide assistance to civilians. Then, they organize a meeting to devise a strategy with which to defeat the villains. They had managed to capture Mummy, but the other three still remain, and although they had already sent an SOS message, the help would take hours to arrive. Izuku devises an action plan that will consist of attracting Nine and their allies to Mount Shiroyama. While some students are tasked with protecting Katsuma, Mahoro, and civilians, the rest will use the terrain to their advantage to separate the villains and defeat them individually.
After recovering from his illness, Nine, Slice, and Chimera are determined to take Katsuma no matter the cost. Slice informs her allies that the students of the U.A. have sheltered all the inhabitants of Nabu in the vast underground caves under the ruins of Mount Shiroyama. When the students see the villains approaching, they put their plan into action. Yuga Aoyama and Momo Yaoyorozu start attacking them from afar with their respective Quirks at full power.
While Nine blocks the attack with his Air Wall Quirk, Slice and Chimera breaks away from the blast, unaware that they are falling right into their trap. The ground under Slice's feet collapses and she falls into an underground cave where Fumikage Tokoyami and Mina Ashido prepare to face her.
In the dark underground cave, Slice uses her Quirk to free herself from the debris that had fallen on her. She stands up, completely unscathed, realizing that the students' plan was to separate her from her allies.
Hidden in the shadows, Mina uses her Quirk Acid to loosen the spikes on the ceiling above Slice, causing the stalactites to fall on the villain, although she manages to dodge them and locates Mina's position, shooting needle-like strands of hair at her. Black Shadow takes the opportunity to attack Slice with Hand Blades, although she protects herself by solidifying her hair. Fumikage asks Mina to leave the rest to him, since that dark cave is his territory. Slice mocks him for his cockiness and prepares for battle.
Fumikage engages close combat with Slice in his Black Abyss. Despite using the darkness to his advantage, Fumikage proves to be unmatched for Slice’s Quirk and her swift combat agility. Confident, she attacks Tokoyami with a barrage of sharped hair, but this is the moment the young hero awaited. With his weapons and Dark Shadow, he manages to defend himself against Slice's attacks, getting close enough to attack her with Abyssal Black Body Sabbath. Although he loses his Hands Blades in the process, Fumikage manages to corner Slice, making an opening for Mina.
Mina uses her signature move, Acid Shot to unleashes a bunch of acid on Slice, who by trying to protect herself from the attack, loses much of her long hair. Fumikage attacks with Dark Shadow, but despite her hair is now short, Slice is still able to it use to attack, and retaliates by using her Quirk to fire a barrage of sharp needles at Dark Shadow, pushing it back. She also shoots her needles at Mina, who is able to evade most of them, but three projectiles stab her thigh and causes her to fall down side of the cave.
Fumikage yells at Mina as she plummets to the bottom of the cave. He approaches her and sees that she's very badly injured and bleeding. Seeing her in that condition infuriates Fumikage, and his Dark Shadow goes berserk, becoming massively monstrous. He viciously attacks Slice, who can barely dodge his blows. Desperate, the villain shoots her hair needles at the ceiling in an attempt to fracture it and allow more light to enter the cavern, but before that happens, she is defeated when Dark Shadow grabs her.
The cavern starts to collapse on top of Fumikage, Mina, and Slice. The sunlight from the sky nullifies Dark Shadow as Fumikage uses his body to shield the wounded Mina while the cavern buries all of them under piles of boulders.
All three are buried under the rocks for a long time, and during that time the rest of the class 1-A students also manage to defeat Nine and Chimera. A large number of heroes arrive on the island to aid the students and inhabitants of Nabu Island, and Hawks himself rescues Fumikage and Mina from the pile of rocks.