While the rest of Class 1-A are asleep, Katsuki takes Izuku to Ground Beta, the site of the Battle Trial where he and Izuku fought for the first time. Katsuki remembers the time where Izuku was a "Quirkless good for nothing" and then suddenly out of thin air he manifested a Quirk and by some miracle he was accepted into U.A. Eventually, Izuku received his Provisional Hero License while he failed. Izuku tells Katsuki that he received his Provisional Hero License for performing well, but Katsuki orders him to keep quiet and let him finish. Ever since the Kamino Incident, Katsuki has been putting the pieces together and has been thinking about it the whole time; Izuku is fully aware as to what Katsuki has discovered. Katsuki states that Izuku received his Quirk from All Might. Having witnessed All For One's ability to steal Quirks and bestow them onto others as well as figuring out that All Might is an acquaintance of All For One, Katsuki hypothesized that All Might also has some form of Quirk transference because he has become weaker ever since coming to U.A and meeting with Izuku. Seeing that Izuku isn't denying anything, Katsuki knows that he is right about Izuku gaining All Might's Quirk.
Izuku knows that Katsuki is correct about him getting his Quirk from All Might and this is his punishment for trying to reveal his Quirk to Katsuki. Izuku asks Katsuki how knowing the truth about his Quirk is going to help him. Katsuki knows that he and Izuku has always looked up to All Might and seeing the person who he thought was a pebble on the side of the road being acknowledged by the person he looks up to is why Izuku is going to fight him here and now.
Izuku is shocked that they have to fight and thinks that they should fight during practice in a rented training grounds. Katsuki tells Izuku that they cannot fight in a class session as the teachers will prevent them from going all out. Katsuki wants to fight Izuku to find confirm what is great about him and why All Might would go so far to help Izuku. Katsuki wants to find out that if Izuku's aspirations are greater than his because he is beginning to doubt if his own aspirations were wrong the whole time. Katsuki charges forward, but Izuku uses One For All Full Cowl to quickly dodge Katsuki's explosion. However, Katsuki's explosion still manages to hurt Izuku's leg. Katsuki comments on Izuku's analytic skills while Izuku is surprised that they are actually going to fight.
Katsuki has just attacked Izuku with an explosion but Izuku barely manages to evade which results in a wound on his leg. Izuku tells Katsuki that his aspirations are not wrong. Katsuki ignores him and attacks Izuku with another explosion to which Izuku successfully dodges using One For All: Full Cowling. Katsuki remembers his childhood where Izuku would always trail along behind him and no matter how many times he would beat him up or scold him, Izuku would still tag along. Katsuki demands that Izuku fights him while remembering that even through they admired All Might Izuku has still managed to get ahead of him. Katsuki remembers All Might telling him during the end of term test that he understood that Katsuki's anger is due to Izuku's sudden growth and tells him that someone at level one and someone at level fifty won't grow at the same rate. Katsuki charges at Izuku with his right arm swinging forward; Izuku prepares to block Katsuki's right swing, but as they get close to each other, Katsuki instead kicks Izuku in the face with his right leg, revealing that Katsuki's right hand swing was nothing more than a diversion. Katsuki takes the opportunity to attack the defenseless Izuku, but Izuku uses One For All: Full Cowling to perform a back handstand which knocks Katsuki away and onto the ground.
Izuku sees Katsuki on the ground and asks him if he is all right. Furious, Katsuki demands once again that Izuku fights him and tells him to stop worrying about him. As he gets up, Katsuki is confused as to how he ended up trailing behind someone who was always trailing behind him his entire life and is angry that the roles are now reversed. Katsuki is angry as to why he became the reason for All Might's end. Katsuki notes that if he had been stronger he wouldn't have been kidnapped and All Might would still be a Hero. Katsuki has been keeping his discovery about the truth of All Might to himself which has been causing him strain and anxiety. Izuku realizes that Katsuki has been carrying that burden of keeping All Might's secret to himself for a while.
Katsuki charges at Izuku. Izuku activates One For All: Full Cowling - Shoot Style and manages to kick Katsuki in the face, which stops Katsuki's charge. While the fight between them may be meaningless since no matter who wins or loses, Izuku understands that the only one who can perceive Katsuki's feelings in this battle now is him and has decided to fight seriously. Izuku activates One For All: Full Cowling throughout his body and tells Katsuki that there is no holding back between them.
Izuku activates One For All: Full Cowling throughout his body and has decided to not hold back against Katsuki. As Izuku declares that he won't become his opponent's punching bag, Katsuki launches himself in the air with an explosion and propels himself to the ground with another explosion, but Izuku is able to dodge with his enhanced speed. Katsuki spins himself around and launches himself at Izuku, which creates and explosion wheel; Izuku continues dodging and sees that Katsuki will close the distance between them after he stops spinning. Izuku attempts to deflect his opponent's hand with a kick, but Katsuki maneuvers behind him and smacks him in the stomach, which sends Izuku reeling back. Not wanting to give his opponent any time to think, Katsuki immediately begins to attack again, but Izuku does a handstand on the railing which allows him to avoid Katsuki. Katsuki grabs Izuku's arm and throws him onto the ground but doing so causes to knock himself into the railing. Izuku has analyzed that Katsuki has managed to polish off his predicting movements faster than him.
Izuku admits that Katsuki has become stronger. However, an angry Katsuki launches an explosion in retaliation, to which Izuku dodges. Izuku charges at Katsuki, but Katsuki uses Stun Grenade. Although Izuku blocks his eyes from the light of Stun Grenade, Katsuki is still able to get ahead of Izuku and land an explosion on him, which launches Izuku in the air. As Izuku lands down, Katsuki reveals that he has despised Izuku's attitude of always getting back up no matter how many times he is beaten down and cannot stand it, believing that Izuku always thought of himself to be superior to him. Izuku is in disbelief that Katsuki thought of him that way. Izuku understands Katsuki as to the same extend his traits such as being amazing at everything was something he was jealous of. Izuku tells Katsuki that he was an amazing inspiring person who was even closer to him than All Might.
Izuku activates One For All: Full Cowling and charges at Katsuki. Katsuki becomes surprised as he sees that Izuku is moving faster than before. Due to his emotions riling up, Izuku has lost some control and the power of One For All increases. Starting to realize that he can now increase the limit of One For All's power, Izuku increases One For All's power from 5% to 8%. Unable to dodge, Katsuki is forced to guard. Izuku strikes the defending Katsuki with a 8% One For All enhanced kick.
Izuku states that he has finally caught up to Katsuki.
Katsuki manages to block Izuku's One For All 8% enhanced kick, but his arm is injured as a result. Izuku is surprised at his own speed and even though he knows that 8% is not much of a difference, he is glad that for a moment he managed to get ahead of Katsuki. Katsuki retaliates with an explosion, which Izuku intercepts with a One For All enhanced kick, cancelling out the attacks and blowing Izuku and Katsuki backwards. While Katsuki gets up, Izuku charges forward and taunts Katsuki, much to Katsuki's anger. Izuku dislikes the part of himself that carelessly runs his mouth whenever he desires to win and despite that, in the end, that bad personality trait is his key to victory. Izuku is in midair and Katsuki decides to engage Izuku in midair as well. While the combatants charge at each other, Izuku ponders that he is not going to play nicely and even though One For All Shoot Style is a way for him not to overuse his arms, he never said that he could not use them. Izuku prepares to use a One For All: Full Cowling enhanced punch with the intend of defeating Katsuki to show All Might why he chose him. Izuku successfully punches Katsuki in the face with his enhanced might, which makes Katsuki bleed. However, Katsuki is filled with determination to not lose either and grabs Izuku. Katsuki uses his Explosion to propel himself and Izuku down to the ground. Katsuki smashes Izuku into the ground using his explosive force.
Katsuki is atop of Izuku and has grappled Izuku's arm and face. Both Katsuki and Izuku are injured badly and breathe for air. After a few moments, Katsuki declares that he is the winner and demands to know from Izuku why he still lost even though he has All Might's power.
All Might tells them to stop and apologizes for eavesdropping on their fight. Katsuki wants to know why he chose Izuku to be his successor. All Might explains to Katsuki that on that day, Izuku was more of a Hero than anybody else and felt that it was his duty to help Izuku stand in the arena whereas Katsuki was already standing in the arena. Katsuki responds that he is weak and because of him not being able to free himself from the League of Villains, All Might is no longer a Hero and is a shadow of his former self. All Might replies that it is not his fault since that all roads have an end and he was going to land up in his pitiful state no matter what, encouraging Katsuki that he is strong and embraces him in an apologetic hug.
Katsuki breaks free from All Might's hug. All Might gives his thoughts on their ideals; Katsuki's obsession with victory and Izuku's obsession over rescuing is crude and because they are lacking in one or the other, they cannot maintain their sense of justice as Heroes. All Might knows that because they have now fought each other they know the truth due to releasing their feelings; if the two of them can recognize each other and honestly raise each other up, they can become the best Heroes who both win and rescue. Katsuki still finds it strange that even though Izuku has All Might helping him he is still losing; Izuku responds that he will become stronger so that he can beat him.
All Might then reveals the full truth of his powers to Katsuki and how it was passed down to Izuku. asks who else knows about Izuku's and All Might's relationship. All Might replies that Mr. Principal and Recovery Girl know the truth about them and only him. Since they have been trying to hide it, Katsuki declares that he will not tell anyone about their relationship and says that the secret of One For All stays with them.