Mt. Lady first debut as a new superhero occurred just as Kamui Woods was about to restrain his opponent with his Lacquered Chains Prison Super Move, when she swooped in, attacking the giant villain with her Canyon Cannon move, and subsequently defeating him. She then introduces herself to the awestruck crowd, proclaiming it to be her first day on the job, and is afterward swarmed by photographers and paparazzi.
She along with Kamui Woods were having trouble dealing with Trapezius Head Gear, as he was holding hostages. That was until All Might showed up and had beaten him and saved the hostages. Although she and Kamui Woods were grateful, they complained that he'll put them out of a job.
Mt. Lady is seen outside the U.A. Sports Festival, having been assigned to guard security. She comments, while eating takoyaki, that all the professional heroes came to watch the event and notes that this year "is gonna be crazy".
After the rules of the Cavalry Battle are explained, Mt. Lady, along with Kamui Woods and Death Arms discuss competition and cooperation in the Hero business. The other hero says that if a hero fails, they lose any chances of surviving, and notes that the Obstacle Race is a perfect example of how sometimes one has to lower someone else to show themselves off, and Mt. Lady mentions that she felt bad for taking out Kamui Woods's enemy on her first day of work, also asking the other hero to stop smoking, while Kamui Woods agrees with the hero. Mt. Lady then comments that sometimes heroes have to cooperate with their concurrence and that the Cavalry Battle is a perfect analogy to that.
Later, while doing her surveillance duties, Mt. Lady watches the fight between Denki Kaminari against Ibara Shiozaki, in which Ibara easily wins. Impressed by her, Mt. Lady tells Kamui Woods that Ibara would make the perfect sidekick for him, but he only responds by telling her to get back to work.
For the Hero Agency Internships, Minoru states that he wants his work place to be with Mt. Lady, causing Tsuyu to think that he is having unclean thoughts, to which Minoru denies. Once there, she makes Mineta her servant, cleaning up and doing other menial labor around her office while she lazed around.
Days later, after the Intership ended, Denki asks Minoru about how his experience was with Mt. Lady, Minoru answers while quivering that he knows the true nature of women now, indicating that his experience with Mt. Lady was traumatic.
Mt. Lady is featured on a daytime talk show where she appears Midnight who is also being interviewed. While Midnight talks about her costumes controversies, Mt. Lady repeatedly interrupts her by poking fun at her need for attention. Eventually, the two come to blows over their ages, much to Minoru's viewing pleasure.
Mt. Lady joins the Police Force and many Pro Heroes in the rescue operation of Katsuki Bakugo.
At the League of Villains' warehouse, Mt. Lady destroys the front of the warehouse. Mt. Lady along with Tora, Best Jeanist and Gang Orca infiltrate the partially destroyed warehouse and apprehend all the Nomus while Tora rescues Ragdoll. Best Jeanist informs Naomasa Tsukauchi that the warehouse has been cleared.
When All For One appears from the shadows, Mt. Lady sees that Best Jeanist is preparing to attack and warns him that the man could be a civilian. Before the Pro Heroes can act, the entire warehouse is destroyed.
Mt. Lady survives the attack thanks to Best Jeanist's quick thinking but is heavily injured. After Izuku and his friends rescue Katsuki, Mr. Compress is flung into the air to catch them. Suddenly, Mt. Lady uses Titan Cliff and intercepts Mr. Compress, which causes them to smash into each other and prevents Mr. Compress from getting to the students. Izuku and Katsuki are surprised at Mt. Lady's intervention. The dazed heroine tells the students to escape before falling down and being left unconscious. Kamui Woods later rescues the unconscious Mt. Lady, telling her she did well.
When the JP Hero Billboard Chart announcement is made, Mt. Lady is ranked No.23. In an interview during the announcement, Mt. Lady comments that being on a team with the No.7 Pro Hero Kamui Woods gives her a lot of encouragement (although privately she is frustrated at not making the top 10 while Kamui did). When the reporter asks about the rumors of Mt. Lady and Kamui having a romantic relationship, she avoids answering the question. Mt. Lady then cried and ran to Death Arms for comfort about Kamui receiving recognition.Class 1-A is learning about how to act in front of media, Mt. Lady is helping since she knows how to act in front of it and tells them to use their special moves in front of the reporters. She tells the class that when they use their special moves in front of the media, they are using it to show villains that it is a warning of their presence, to heroes a key to team building, and to the citizens that they are safe. Mt. Lady then praises class 1-A for doing a great job but when Izuku Midoriya tried he becomes stiff but when she mentions that his power is similar to All Might, he bursts out talking.