A giant monster is terrorizing the city. Suddenly, All Might appears and defeats the monster with ease. The public are awed at All Might's strength. Seeing that everyone is unharmed, All Might takes his leave. A person in the crowd, Koichi Haimawari who is a male of 19 years of age, is inspired by heroes like All Might.
Koichi touches the ground in order to use his Quirk, Slide and Glide, which allows him to slide on the ground; the speed of his sliding is as fast as a bike. However, a police officer stops Koichi and berates him for using his Quirk when public usage of Quirks is forbidden and tells him that since everyone has different Quirks, using Quirks in public is forbidden in order for everyone to live well with each other. After the police officer leaves, Koichi runs towards his next destination and is annoyed that he must follow the rule of unable to use Quirks in public.
Koichi crashes into a group of thugs, spilling Soga Kugizaki's juice. Souga orders Koichi to apologize by getting down and groveling. Soga wanted to humiliate him for it, and prepare to step on Koichi, but the boy uses his "super move" Kowtow Evasion to slides backwards, surprising Soga. Koichi slides away and escapes.
Koichi sees another group praising a freelance idol, Pop☆Step. Koichi notes that Pop☆Step is taking a big risk in being a freelance idol since she does not have a permit. Despite her songs not being great, the aspect that stands out is her ability to fly which is what attracts some people to become her fans. A police vehicle is passing by, so Koichi warns Pop☆Step, who decides to end her live performance and flies away while Koichi prepares to slide to his place of work.
Koichi works at a convenience store; the manager is not pleased with Koichi being late and deducts his pay. Customers arrive; however, they are the same group of thugs that Koichi encountered earlier. Soga becomes angry at seeing Koichi again and takes him outside. There, Soga beats Koichi up; Koichi is not able to fight back because Soga uses a Quirk called Spike, which creates sharp spikes from his knuckles. After being forced to buy a juice for Soga, Koichi is annoyed at being beaten up. Koichi changes into his "suit" which is an All Might-styled jacket with a hood and wears a mouth mask. Koichi decides to deliver justice on his own accord without being bogged down by the law.
Koichi starts doing good deeds for the public such as returning dropped items, giving directions, helping people get onto trains, being a cameraman, and recycling. The citizens thank Koichi and refer to him as Nice Guy. Koichi feels overjoyed in helping people as it relieves him of stress and makes him feel warm inside. With his good deeds done for the day, Koichi begins walking home. Suddenly, a person gives Koichi juice to drink. The person giving him the juice is Pop☆Step. She thanks him for warning her about the police and followed him in order to properly thank him, but mocks him for being weak, to which he defends himself as being poor at dealing with violence.
She finds it ironic that he is wearing an All Might hoodie, but is bad at fighting. Koichi wears the All Might hoodie because it symbolizes his ideal in being useful in his own way. After they scrutinize each other for their objectives, Pop☆Step begins to leave but bumps into Soga. The thugs recognize her as the online idol and begin mocking her. Koichi tries to stop them, but the thugs ignore him. Koichi sees tears in Pop☆Step's eyes and cannot ignore her plea for help. Koichi theoretically wonders how he can handle the situation; use his Slide and Glide to trip two of the thugs and take out the leader by tackling him so that Pop☆Step can fly away.
Koichi decides to put his plan into motion and slides into Moyuru Touchi, trying to trip the thug, but fails. Moyuru throws Koichi to the ground. The thugs turn their attention to Koichi and Soga scratches Haimawari's face with spikes from his foot. Soga decides to finish off Koichi for annoying him and to strip down Pop☆Step.
As Soga prepares to strike Koichi with his spikes, someone crashes down onto the trash which stops Soga. The person gets up from the trash heap, revealing to be a muscular old man, as Soga wonders what is going on. Suddenly, the old man punches Soga which knocks him down to the ground, surprising Koichi. Moyuru and Rapt are shocked at what transpired and ask for the old man's motivations.
The old man tells the thugs that he is called Knuckleduster and specializes in dealing with hoodlums like them. Knuckleduster suddenly asks Rapt if he has drugs in his possession and orders him to show his tongue. Before he can answer, Knuckleduster punches him hard in the stomach and sticks his tongue out, checking that it does not have any discoloration. After finishing him, he easily defeats Moyuru and verifies that his tongue is not discolored either.
Knuckleduster turns his attention to Koichi and praises him for his efforts, telling him that he can become a real Hero if he works with him. Koichi shows no interest, but Knuckleduster can see through his lies and knows he is someone who cannot abandon people in need like All Might. Koichi admits that his Quirk is not useful and could never pass the Pro Hero Exam. Knuckleduster does not care about whether Koichi has a powerful Quirk or license because they have absolutely nothing to do with justice. Knuckleduster believes that true Heroes take action when something rises up before them. Koichi realizes that Knuckleduster is unlicensed.
Suddenly, Soga gets up, takes Pop☆Step hostage, and threatens to claw her face off with his spikes. Unable to let him get away with his atrocious act, Koichi charges at Soga and knocks him down, allowing Pop☆Step to fly above for safety. Knuckleduster punches Soga into the wall, knocking him out. Knuckleduster sees that Soga is not in possession of the drug he is looking for and makes a copy of his ID.
After defeating the thugs, Knuckleduster informs Koichi that there are more ways to be a Hero than what the world says; Knuckleduster is a Hero because punishing evildoers is refreshing, decides to adopt Koichi as his disciple. However, Koichi finds Knuckleduster to be dangerous and is not sure about joining him.
Later on, the thugs walk in an alley and are badly injured courtesy of Knuckleduster. Soga is annoyed and angry, promising to kill Koichi and Knuckleduster next time, although Moyuru suggests not to get involved with them. Out of nowhere, a man in a suit appears before the thugs and offers them "splendid" medicines.