At some point in his life, Atsuhiro worked as an entertainer before turning to a life of crime.
Mr. Compress is recruited to the Vanguard Action Squad of the League of Villains. He is one of the last villains to arrive at the Beast's Forest. Mr. Compress takes the students by surprise when he introduces himself while balancing on a tree branch. He explains that he took Katsuki with his "magic". Angry, Izuku demands that the villain return Katsuki.
Mr. Compress replies that Katsuki's talents would be wasted as a hero, and says Izuku is arrogant for trying to claim Katsuki for his own. Shoto tries to freeze the villain but he evades and continues taunting the young heroes. He says Katsuki is drowning in a society of heroism and that the Vanguard Action Squad wishes to show him another way.
Mezo notices that Fumikage is missing as well. Shoto wonders what the villain's Quirk could be and warns him not to underestimate the boys. Mr. Compress explains he improvised on taking Fumikage because he defeated Moonfish so easily, and violently. Shoto tries to freeze Mr. Compress with a massive ice wave, but the showman avoids it. Mr. Compress admits he's not much of a combatant and then radios the Vanguard Action Squad to meet at the rendezvous point.
Mr. Compress moves quickly through the treetops towards the meeting point. Izuku, Shoto, and Mezo tackle him out of the air and slam him into the ground at the planned rendezvous area. Dabi warns his ally to get out of the way. Mr. Compress complies and compresses himself into a marble. After Dabi forces them away, Mr. Compress reverts to his normal form. He complains that they ruined his exit and Dabi asks about Katsuki. Mr. Compress rummages through his pockets and finds that the marbles are missing. Mezo reveals that he stole them and surmises that Katsuki and Fumikage are sealed inside them.
The boys flee and Dabi wants to pursue them, but Mr. Compress tells him to wait. Kurogiri arrives to take the villains back to safety. Mr. Compress tells Dabi he was impressed with the boy's efforts so he allowed them to gloat. The showman turns his attention to the boys and tells them that he flashed those fake marbles to hide the real ones. He moves his mask aside and reveals he has held the real marbles inside his mouth the entire time. Mr. Compress reverts the fake marbles into ice, revealing that he took Shoto's ice and compressed it to fool his pursuers.
Before entering Kurogiri's Warp Gate, Mr. Compress takes one final bow. This leaves him open to a surprise attack from Yuga, who is hiding in the bushes. Yuga's navel laser blasts Mr. Compress in the face, breaking his mask and forcing the marbles out of his mouth. Dabi catches one of them and orders Mr. Compress to release them. He reverts Katsuki and Fumikage back to normal after complaining that Yuga ruined his finale. Dabi holds Katsuki by the neck and drags him through the portal, completing the League of Villains' mission.
After watching the video clip about U.A.'s public apology, Tomura understands why society is criticizing U.A. for their failure and that is because the current Hero society is not just. Spinner agrees that the current Hero society is not just because the modern Heroes are only doing their job for compensation and not out of selflessness. Tomura explains that the League of Villains are fighting for a just society and intends to win this battle.
Tomura orders the removal of Katsuki’s restraints. Tomura wants to treat Katsuki as an equal and is aware that Katsuki knows he has no possibility of winning. As Twice removes the restraints, Mr. Compress apologizes to Katsuki for forcibly kidnapping him and explains that the League of Villains are not just a group of hoodlums perpetuating crimes, nor did they casually abduct him; he goes on by saying that everyone in the League of Villains is shackled by the current society and hopes that Katsuki understands their discrimination.
Katsuki’s restraints are removed. As Tomura approaches Katsuki, Katsuki attacks him with his Explosions. Katsuki tells the League of Villains that it is pointless to try and make him change his mind as he has already been won over by the way All Might looks when he wins. Katsuki says that from the beginning he has dreamed of becoming a Hero and surpassing All Might and nothing they say will change that.
Katsuki tries intimidating his captors, but Mr. Compress along with the rest of the Vanguard Action Squad are not intimidated; Mr. Compress states that if Katsuki was moronic, he would have listened to them and is disappointed in Katsuki's decision to go against them.
Tomura orders Mr. Compress to use his Quirk on Katsuki again. Mr. Compress is impressed with Katsuki's stubbornness. Before he has the chance to, All Might breaks in with Kamui Woods swinging in, and restrains Mr. Compress along with the other League of Villains with his Lacquered Chains Prison. Mr. Compress realizes that U.A.'s public broadcast apology was just a diversion to catch him and his fellow villains off guard.
Out of nowhere, Nomus appear from a mysterious back liquid which catches the Pro Heroes off guard. Mr. Compress along with the League of Villains are teleported by the mysterious black liquid to the League of Villains' destroyed warehouse where All For One is.
All For One forcefully activates Kurogiri's Quirk which creates a portal for the League of Villains to escape through. Mr. Compress uses his Quirk on the unconscious Dabi and tells Tomura that they need to leave. Seeing that Katsuki won't go with them willingly, Mr. Compress, along with Twice and Himiko, battle Katsuki but Katsuki fends them off with Explosions.
After Katsuki is rescued by Izuku, Tenya, and Eijrou, Mr. Compress along with Magne and Spinner hatch a plan to recapture Katsuki. Magne magnetizes Mr. Compress and Spinner pushes him, causing Mr. Compress to fly at Izuku's group. Suddenly, Mount Lady uses Titan Cliff and intercepts Mr. Compress, which causes them to smash into each other, preventing Mr. Compress from getting to the students. Mr. Compress falls to the ground and becomes unconscious due to Mount Lady's attack.
Mr. Compress, along with Tomura and the Vanguard Action Squad, are forcefully magnetized by Magne's Quirk, courtesy of All For One; Mr. Compress is sucked into Kurogiri's Warp Gate and teleported away. Mr. Compress later recovers along with the rest of the league during the aftermath of the battle.
Once the League of Villains regain their momentum, Mr. Compress contacts Himiko after the Provisional License Exam ends. Mr. Compress expresses concern for Himiko and tells her to be more careful on revealing her appearance in the public.
Himiko assures Mr. Compress that she always is cautious enough to avoid getting caught. Along with that, Himiko reveals that she managed to collect a dose of Izuku's blood, much to the delight of Tomura, who plans his grand return.
After the capture of All For One, the League of Villains has lost a lot of strength, therefore, Tomura orders that the members of the League look for suitable people to join them in their ranks. Twice meets Overhaul, leader of Shie Hassaikai, and invites him to an abandoned factory to meet with the others.
Once here, Tomura recognizes Overhaul as the young boss of the Shie Hassaikai, one of the yakuza that All For One showed him before. Himiko Toga asks how someone involved in organized crime is different from the League of Villains. Mr. Compress explains to Himiko that the yakuza come from an old era of villains where there were a number of frightening organizations that ran the underworld, but the rise of Heroes started to put an end to those underworld villain organizations. Following the rise of All Might, the yakuza because nearly extinct and live under constant surveillance. Ashamed, even Overhaul is inclined to agree on the sorry state of the yakuza.
Overhaul is unimpressed with the League of Villains. He explains that with All For One's downfall, someone will eventually become the next ruler of the underworld. However, Tomura replies that he will become the next underworld ruler after he gathers more members and crushes the current Hero society. Overhaul argues a goal with no plan is a delusion and says Tomura wasted first-class soldiers like Stain, Muscular and Moonfish. Overhaul reveals that he has a plan and he wants the League to join him. He needs the League of Villain's name to to gain financial capital for his plan that will allow him to be the new ruler.
As Tomura orders Overhaul to leave, Magne rejects this proposal and magnetizes Overhaul, bringing him into Magne's range. Magne hits Overhaul on the head with her weapon, to which Overhaul responds by touching Magne. Overhaul's physical contact causes Magne to blow up, much to the League of Villains' shock. Overhaul blames the League for throwing the first punch and dislikes the blood running down his face.
Mr. Compress charges forward and touches Overhaul but his Compression Quirk does not activate due to being shot in the arm. Overhaul is enraged that he has been touched and completely disassembles Mr. Compress's left arm. Overhaul then calls his subordinates, who come crashing in. Seeing that both of their organizations have suffered casualties with the deaths of their respective members, Overhaul ceases fighting and leaves, wishing to talk with Tomura again after he has calmed down.Twice and Himiko want to avenge their allies and kill him. Although he is also angry, Tomura orders them to stand down, allowing the Shie Hassaikai to leave the place. Twice checks on Compress's condition and Himiko tells they need to get Compress to a doctor. Later, they get in touch with Giran who provides Compress with a robotic arm to replace the one he lost.
After meeting overhaul again, Tomura signs an alliance between the League and Shie Hassaikai. In exchange for Overhaul explaining his plan, which is to sell special bullets that allow erase Quirks, he give him Twice and Toga. Although both are not initially happy with Tomura's decision, but he manages to convince them that this is the best way to get revenge. 
And only a few days later did that opportunity come. At one point, a group of heroes led by Sir Nighteye assaults the base of Shie Hassaikai, a moment that is used by Toga and Twice to betray Overhaul, and help the heroes. After a hard battle, all members of shie hassaikai are arrested and the criminal organization dismantled. Using a clone of Mr. Compress, Twice and Toga wanted to take advantage of the raid to obtain the source with which Overhaul manufactured his bullets, a girl named Eri, but they fail and are forced to withdraw.
However, they tells their allies where Overhaul and the perfected Quirk-Destroying bullets are. With their indications, Mr. Compress and the League of Villains find and apprehend the police van escorting Overhaul. Sand Hero "Snatch" confronts them but after a brief skirmish, Mr. Compress compresses him into a sphere with some of Dabi's flames. The van transporting Overhaul crashes after hitting a boulder Mr. Compress threw into the road.
Tomura confronts Overhaul and tells him how much he hates him. Mr. Compress appears from behind and agrees with the statement by compressing part of Overhaul's left arm, severing it at the wrist as an act of revenge. Tomura decays Overhaul's right arm before cutting it off and taunts the powerless yakuza about how he wanted others to lose their Quirks but now he himself is one of them.
Overhaul is left armless, hepless and horrified while the League of Villains walks away from the wreckage with the Quirk-Destroying bullets.
One month before the Hero Billboard Chart JP announcement, the League of Villains— minus Dabi— raid the base belonging to the Creature Rejection Clan. In search of valuables to sell, Mr. Compress rifles through some knickknacks that are on display, explaining that the League is strapped for cash. The CRC attack the League in retaliation. When a member of the religious group attempts to restrain him from behind, Mr. Compress uses his quirk to compress his attacker's arm. The League slaughters the CRC, but find nothing worth selling. While Toga laments over one of her broken blood drawing needles, Mr. Compress mentions that his prosthetic arm is beginning to get squeaky as well, and that they should have Giran replace them.
After the raid, the League of Villains take refuge at a rundown construction site. During a confrontation between Tomura and Spinner, Mr. Compress chimes in to complain that they would all be eating sushi right about then, had they worked with the Shie Hassaikai. A rumble shakes the building, ending the disagreement. The League rushes outside of the base to see Gigantomachia burst from the ground.
Distraught and inconsolable, Gigantomachia attacks the League. Mr. Compress is easily tossed aside by the beast, losing his hat and the hand of his prosthetic arm in the process.
Mr. Compress suggests they would use the high-end Nomu that Dabi was testing, proclaiming that he is a Jack-of-all-trades. And asks Tomura that why he turned to the doctor. Tomura asks him how much time it takes for Gigantomachia wakes up, and he replies that it would be two hours and thirty-five minutes. Later, when they arrive on the outskirts of Deika city, Mr. Compress and the other League of Villains members travel to Deika City to rescue the broker Giran from the Meta Liberation Army. Where they encounter the approaching pro hero Slidin' Go on the cities outskirts and takes them to the city to meet the leader of the Meta Liberation Army. He replies that nobody is there, and the pro hero Slidin' Go says to them that the city is not under his jurisdiction and that the day is special. Spinner, wondering who the one that snapped his fingers is, Mr. Compress reminds the League of Villains member that Koku Hanabata is a member of the Heatseekers Party as he and the other League of Villains begin to take the offensive against the 110,000 soldiers en massed towards them.
Spinner later asks him how much remaining time it would take for Gigantomachia to wake up and he replies that it would be one hour and twenty minutes. He also sees that Koku Hanabata is in an election van rallying people to his cause like a religious bishop. As Dabi and Geten's powers of fire and ice collide, he proclaims that he should show some moderation. He then thinks to himself that the League of Villains have split up into different groups.
Mr. Compress later begs Dabi for help, who is being overwhelmed by Deika City soldiers, who says to him that he is lacking in compassion. Dabi tells him that he should ask them. He later gets help from all of Twices' clones, who speak all at once for help, telling them to put a sock in it, proclaiming them to be out of a heroes story. Twice asks him how much time left it takes Gigantomachia to wake up. He says to them that they have one hour and five minutes. He also proclaims that if Geten was to face Gigantomachia in a fight, he would be a challenge.
Mr. Compress informs Dabi that they underestimated him and Gigantomachia wasn't fighting seriously against them and notes that he is unstoppable.
Mr. Compress asks himself that why Gigantomachia had to wake up so early, and that he and rest of the League of Villains would clash against him and they would be done for. He immediately contacts Daruma Ujiko so that they can warp them out of Deika City with the Nomu Johnny's warping Quirk, saying that he is too much and that they are going to die. The doctor refuses their help, thinking that they are going to get his little John killed. He proclaims that he is lying, and that he has been using it like crazy. He then questions him if he is going to leave Shigaraki to die and that he is All for One's successor.
Once Re-Destro was defeated and bestowed control of the army to Tomura, Mr. Compress ate sushi with his comrades after the battle. Mr. Compress is pleased with this, as Dabi remarks that he did not do much while he defends himself.
He and the rest of the League came on stage when Tomura announced the Meta Liberation Army and League of Villains will become the Paranormal Liberation Front (which Spinner and Re-Destro coined together), becoming one of its Lieutenants. After the speech, he is surprised when Tomura collapses from his injuries, something that he remarks isn't surprising. Mr. Compress realizes Tomura is talking to Dr. Ujiko.