Two years prior to the current story, Kota's parents sacrificed themselves to save civilians from the villain Muscular. Believing they died a truly heroic death, many supporters praised Water Hose. Kota however, was devastated by their deaths. Kota believed that his parents chose their work over him, and developed a twisted view of the world of heroes.
Kota was taken in by the Wild, Wild Pussycats, a hero team that Shino Sosaki (his last known relative) is a part of. Despite despising heroes, Kota listens to his relatives and the Pussycats because he has nowhere else to go.
Students from U.A. High arrive at the Pussycat's reserve to train for their summer break. The Pussycats introduce themselves but Kota remains silent. Pixie-Bob sends the students into the Beast's Forest and fights them using her quirk to create dirt monsters. Kota watches the start of the fighting, but Mandalay tells him they're going back to base camp. Kota thinks their training is pointless, and that the students are stupid for wanting to become heroes. He snarls and leaves with Mandalay.
Class 1-A doesn't arrive at base camp for several more hours. Izuku asks Pixie-Bob who's kid Kota is. Mandalay clears up the confusion and explains that Kota is her cousin's child. Mandalay asks Kota to introduce himself, but he remains silent. Izuku walks over and greets Kota personally. Izuku outstretches his hand, but Kota instead greets him with a swift punch to the groin. Tenya runs up to check on the blindsided Izuku and yells at Kota. Kota angrily replies that he refuses to hang around a bunch of wannabe heroes and storms off.
At dinner, Kota helps Mandalay with a box of vegetables. Later on, she places him on the wall splitting the boy's hot springs from the girl's. When Minoru tries to scale this wall in order to peep on the girls, Kota catches him at the top of the wall and tells him if he's going to be a hero, he needs to learn how to be a decent person. He pushes Minoru down the wall, garnering praise from the girls. Kota mistakingly looks back and sees the nude girls, causing him to faint and fall over the wall. Izuku catches him and brings him to Mandalay's office.
Mandalay thanks Izuku for saving him and explains Kota fainted from the fear of the fall. Izuku asks why Kota seems to hate heroes. Pixie-Bob enters the room and tells Izuku that Kota's parents were pro heroes who died in the line of duty. To Kota, his parents abandoned him for their hero work.
The next day, Kota silently watches Izuku train with Tora from behind a tree. Later on, Kota opts not to eat dinner with everyone and ventures to his personal hideout. He's displeased when he realizes Izuku followed him there. Izuku brings him a plate of curry, but Kota says he doesn't need it and just wants Izuku to leave.
Izuku asks if Kota's parents were the Water Hose heroes, irritating the boy even more. Kota says people using quirks to show off and calling themselves heroes and villains are what's wrong with the world. Izuku tells Kota a story about his friend who couldn't manifest a quirk and how much he wanted to be a hero. Kota refutes Izuku and tells him to leave once again. Izuku leaves Kota alone with the plate of curry. During that night, Kota recalls Shino telling him that one day he'll meet someone that will help him understand heroes. Then he's distracted by the flames that have lit up the mountainside, shocking him with the chaos. A masked villain sneaks up on him from behind.
The villain says that he's surprised to find someone not on his hit list. Paralyzed in fear, Kota begins to cry and backs away from the man. The masked man prepares to kill Kota for his hat, just as the young boy recognizes him. He's the villain Muscular, the very same villain that murdered both of Kota's parents. Izuku suddenly arrives and rescues Kota just in time. Izuku promises to save him and engages Muscular. Kota watches in horror as Muscular overwhelms Izuku. Just before Muscular finishes Izuku, Kota throws a rock and asks Muscular a question.
Kota asks Muscular if he toyed with his parents Water Hose like he's doing to Izuku. He tells Muscular that he's what's wrong with the world. Muscular approaches Kota and tells him he's wrong for shifting the blame. The villain explains that he wanted to kill people and his parents wanted to protect them. He mocks their death by saying that the only tragedy is when a hero doesn't do they set out to but doesn't blame them for his lost eye. He then tries to kill Kota but Izuku rushes in and attacks Muscular from behind. He yells at Muscular for not taking the blame. Izuku explains that it's not a matter of whether or not heroes can do it. It is simply a heroes job to risk their lives to make their words into reality and then strikes Muscular with a maxed out punch.
Izuku's punch destroys part of the cliffside and nearly knocks Kota off on accident. Fortunately, Izuku catches Kota in time using his teeth and brings him back on land. Kota wants to thank Izuku, but he's horrified by the damage Izuku has taken for him. Muscular suddenly recovers from the attack, having used his muscles to absorb the damage. Muscular says he's going all out and attacks Kota and Izuku at full power. They narrowly evade a few of his attacks. Izuku tells Kota to flee while he holds the bloodthirsty villain back. Kota replies that Izuku is too injured to fight and they should both run away. Izuku reminds Kota that everything will be okay.
Muscular rushes them both at full strength and Izuku barely holds him back. Izuku tells Kota to run while he's being crushed by Muscular's muscles. Kota splashes Muscular using his quirk and distracts him by yelling for him to let Izuku go. Izuku takes advantage of this distraction and tells Muscular that he will never hurt Kota. Kota watches in amazement as Izuku defeats Muscular with one spectacular attack.
Kota cries as he remembers Mandalay talking to him about heroes. She said that he would meet someone that would risk their life for him. He questions why Izuku would do that for someone he doesn't know. Kota realizes heroes risk their lives to save people so that one day someone can call them “My Hero”.
Izuku slowly recovers from the fight and tells Kota there are still more people he can save. Kota worries about Izuku's condition but Izuku is only focused on helping others. He even asks Kota to help his friends by using his quirk to put out the forest fires. Izuku carries Kota through the forest until he runs into his teacher: Shota Aizawa.
Izuku trusts Kota's safety to Shota. Shota rushes Kota to the facility and Kota cries on their way there. Kota wonders if Izuku will be alright, crying that he did not get a chance to apologize. Shota tells Kota that Izuku will be alright and advises him to thank Izuku the next time he sees him.
At the facility, Shota asks Vlad King to look after Kota. The Vanguard Action Squad's attack ends after Katsuki is captured.
Two days later, the doctor at the hospital Izuku is currently in hands him a letter from Kota. The letter thanks Izuku for saving him and hopes that Izuku gets well soon so that he can thank him in person.
When the Pussycats visited U.A., Kota accompanied them to the dorms where he met Izuku again. The latter was happy to see him and thanked him for the letter before Shino soon pointed Izuku out to the new shoes Kota has, which looked exactly like Izuku's shoes. Kota became embarrassed after Izuku pointed out the match.