"Exceptional Abilities" is a never before seen mysterious mutation that quickly spread among people. According to one theory, it was an unknown virus that was spread throughout the world carried by mice and is believed to be the origin of Quirks. However, there is no clear evidence that backs up this theory.
In the present, Kai Chisaki claims that neither Izuku Midoriya nor Eri herself understands the true power behind Eri's Quirk and through extensive research, he was able to successfully extract Eri's power and bring it to its pinnacle; the result is the Quirk-destroying bullet, which has the power to extinguish one's Quirk Factor and return them to normal. Kai reconstructs the surrounding area and attacks Izuku with stone columns. However, Izuku's greatly enhanced speed thanks to One For All: Full Cowl - 100% enables him to dodge with ease. Izuku delivers a kick packed with massive strength and sends Kai flying into the air.
Izuku feels that Eri's power is getting stronger due to her being unable to control it, similar his inability to control One For All when he received it. Himiko Toga witnesses Izuku's strength and is mesmerized by it while Twice wonders the whereabouts of the Mr. Compress's clone.
In the Shie Hassaikai's basement, the Mr. Compress clone is held down by Ryuko Tatsuma, who sends the weightless Ochaco Uraraka and Sir Nighteye to the surface, telling Ochaco to get Sir Nighteye to an ambulance. Meanwhile, Kai has been sent straight into the air by Izuku's great strength, having been injured as a result, and starts thinking about the past.
The Shie Hassaikai's boss criticized Kai or beating up someone, to which Kai replied that he was simply protecting their turf. Kai stated to his boss that they must make their presence known to the world, but the Shie Hassaikai's boss knew that Kai had started a venture dealing with Quirk related drugs and had told him not to get involved and while he understood that he was simply repaying the kindness after the boss saved him, he must not go overboard nor must he stray from his path. Kai remembers talking to Hari Kurono about the Shie Hassaikai becoming extinct if they do not do something; Hari replied that the idea of yakuza restoring the underworld is an unrealistic dream. However, Kai refused to waver and planned to restore the Shie Hassaikai to its former glory.
One day after having done extensive research on Eri's Quirk, Kai brought forth his plan to the Shie Hassaikai's boss; Kai planned on selling the Quirk-destroying bullets to Villains who would use them on Heroes and after a while, the yakuza would distribute a serum that would undo the damage done and restore the lost Quirks to the Heroes. These products would be at a high price. Therefore, with the Villains having the Quirk-destroying bullets, the Heroes having the serum, and Eri in the middle, the Shie Hassaikai can monopolize control of the market, earning massive profit and eventually emerging from the shadows.
However, the Shie Hassaikai's boss had already refuted Kai's plan and questioned his morality regarding humans. The boss advised Kai to leave if he was going to disobey their way of thinking. Kai did not plan on going anywhere as all he wanted to do was repay the boss for taking him in and despite the boss's refusal, told him to watch from the sidelines as he went through with his plan. Kai blamed Quirks for bringing forth Heroes that put the Shie Hassaikai's boss in a corner and with his plan he could restore the Shie Hassaikai back to its former glory.
Izuku jumps towards the airborne Kai who has healed his injuries by reconstructing himself and slashes at Izuku with one of his claws. However, Izuku evades with ease and knows that Kai can repair himself with his Quirk through disassembling and reassembling at a fast rate, but he plans on using the great power of One For All: Full Cowl: 100% to close that gap and beat him before he gets the chance to recover with his Quirk. Izuku charges towards Kai and starts pummeling Kai's monstrous stone body, shattering it as Kai is unable to counter attack. Izuku reaches Kai's own body and pummels away. Izuku questions that if he cannot save one little girl right in front of him, then he can never become a Hero that saves everyone.
Ochaco and Sir Nighteye have reached the surface and bear witness to Izuku and Kai's battle. Ochaco questions Sir Nighteye's vision about Izuku dying. Sir Nighteye replies that it is the unchangeable future he saw but is surprised that events are playing out differently.
Izuku reaches Kai and punches him in the face with enough force that not only sends Kai reeling but also breaks off his plague mask.