The Naruhata Vigilantes & Shota Aizawa vs. Mario Kugutsu, Soga Kugizaki, Moyuru Tochi & Raputo Tokage, is a battle between Koichi Haimawari and Kazuho Haneyama against Mario Kugutsu, Soga Kugizaki, Moyuru Tochi & Raputo Tokage. Later, Knuckleduster and Shota Aizawa come to help them.
After being beaten by Knuckleduster, Soga Kugizaki, Moyuru Tochi and Raputo Tokage meet a mysterious man in a suit who gives him a drug called Trigger. While Moyuru and Raputo inject themselves the drug and turned into Impromptu Villains, Soga decides to save his dose for later.
Knuckleduster explains Koichi the matter about Trigger, its relation with the recent incidents with villains, and its secondary effects on consumers, Knuckleduster takes Koichi to search for clues about the drug, using violence and intimidation on whatever he considers suspect, what which surprises Koichi. During their search, they encounter Pop☆Step, and Koichi explains her the situation.
Sudenly, Knuckleduster spots a salesman and prepares to interrogate him. Koichi tries to stop him, and accidentally drop the salesman’s suitcase which has Hero figures. Knuckleduster finds this suspicious, but Pop☆Step and Koichi try to stop the old man to no avail. Knuckleduster tries to make man confess by force but is stopped by Aizawa, starting a fight between them.
The salesman leaves in a hurry, but Pop☆Step realizes that she has seen him before. Seeing some pictures, She discovers that he has been present in several villain disturbances, and tells Koichi that he is really suspicious. Koichi and Pop☆Step chases after the salesman but are stopped by Soga, Raputo, and Moyuru. Soga prepares to take his revenge on Koichi and injects himself with Trigger, turned into another impromptu Villain.
Due this situation, Koichi and Pop☆Step decide running away, being persecuted by the transformed thugs. Pop☆Step chases after the suspicious salesman, being persecuted in turn by Raputo. For his part, Meanwhile, Koichi tries to escape as he can from Soga and Moyuru, causing panic in the streets.
Mocking his cowardice, Soga attacks him transforming into a spiked ball. Koichi manages to dodge it, but is knocked down at the feet of Moyuru. When he was about to attack him, Kd suddenly appears behind Moyuru, smashing a brick onto his head, knock him out. Soga attempts to attack Koichi, but Shota uses his quirk and his Capturing Weapon to stop the thug in his tracks. Seeing that Erasing Hero is handling the thugs, Knuckleduster and Koichi decide to go and find Pop☆Step.
Pop☆Step continues chasing after the salesman, with Raputo behind her. Raputo kicks her, causing her to fall on the salesman, who drops his suitcase again. The salesman picks up the All Might doll, pops off its head, and uses it to inject himself with Trigger, grows into a colossal giant with four arms.
The giant grabs Pop☆Step and Raputo with his hands, swinging them about. Knuckleduster attacks him in the face, but the colossal salesman retaliates and smacks Knuckleduster into the ground. However, Knuckleduster's attack causes him to release Pop Step, who falls from a considerable height, being unable to stop due to no footholds. Seeing this, Koichi slides up the side of a building and jumps off towards Pop☆Step. The reason Koichi decided to help her is because even though it is far too late to become a Hero, he still wants to soar through the skies like her. Instead of being caught by Koichi, Pop☆Step uses him as a platform for her Leap Quirk.
As Pop☆Step flies onto a building for safety, Koichi begins falling to the ground. The colossal salesman takes notice of Koichi and prepares to palm him. With quick thinking, Koichi decides to slam into the colossal salesman's palm and activates his Quirk, shifting the trajectory of his fall and landing onto a pile of garbage, safe and sound. However, the colossal salesman launches a punch at Koichi.
Suddenly, the colossal salesman starts shrinking and returns back to normal. Shota activated his Erasure which forced the salesman's Gigantification Quirk to become disabled. Shota wraps his cloth around the salesman.
After this incident, the Police Force arrive and arrest the salesman and the three thugs. Shota thanks Knuckleduster for his assistance but warns him about the dangers of his vigilante activities. Knuckleduster replies that Heroes need people like him to deliver justice without restrictions.
Meanwhile, in a back alley, Pop☆Step is relieved that Koichi is alright. She was going to thank him, but since he is annoying her she does not, while she blushes. Knuckleduster appears pleased by Koichi actions. Knuckleduster knows he still aspires to be a Hero, and encourages Koichi to chase after his aspiration to be a Hero. Thus, Koichi's life as a Vigilante begin from a lonely back alley and he would eventually go on to reach for greater heights.