The seemingly unimpressive Saitama has a rather unique hobby: being a hero. In order to pursue his childhood dream, Saitama relentlessly trained for three years, losing all of his hair in the process. Now, Saitama is so powerful, he can defeat any enemy with just one punch. However, having no one capable of matching his strength has led Saitama to an unexpected problem—he is no longer able to enjoy the thrill of battling and has become quite bored. One day, Saitama catches the attention of 19-year-old cyborg Genos, who witnesses his power and wishes to become Saitama's disciple. Genos proposes that the two join the Hero Association in order to become certified heroes that will be recognized for their positive contributions to society. Saitama, who is shocked that no one knows who he is, quickly agrees. Meeting new allies and taking on new foes, Saitama embarks on a new journey as a member of the Hero Association to experience the excitement of battle he once felt.

The appearance of quirks, newly discovered super powers, has been steadily increasing over the years, with 80 percent of humanity possessing various abilities from manipulation of elements to shapeshifting. This leaves the remainder of the world completely powerless, and Izuku Midoriya is one such individual. Since he was a child, the ambitious middle schooler has wanted nothing more than to be a hero. Izuku's unfair fate leaves him admiring heroes and taking notes on them whenever he can. But it seems that his persistence has borne some fruit: Izuku meets the number one hero and his personal idol, All Might. All Might's quirk is a unique ability that can be inherited, and he has chosen Izuku to be his successor! Enduring many months of grueling training, Izuku enrolls in UA High, a prestigious high school famous for its excellent hero training program, and this year's freshmen look especially promising. With his bizarre but talented classmates and the looming threat of a villainous organization, Izuku will soon learn what it really means to be a hero.

At UA Academy, not even a violent attack can disrupt their most prestigious event: the school sports festival. Renowned across Japan, this festival is an opportunity for aspiring heroes to showcase their abilities, both to the public and potential recruiters. However, the path to glory is never easy, especially for Izuku Midoriya—whose quirk possesses great raw power but is also cripplingly inefficient. Pitted against his talented classmates, such as the fire and ice wielding Shouto Todoroki, Izuku must utilize his sharp wits and master his surroundings to achieve victory and prove to the world his worth.

As summer arrives for the students at UA Academy, each of these superheroes-in-training puts in their best efforts to become renowned heroes. They head off to a forest training camp run by UA's pro heroes, where the students face one another in battle and go through dangerous tests, improving their abilities and pushing past their limits. However, their school trip is suddenly turned upside down when the League of Villains arrives, invading the camp with a mission to capture one of the students. Boku no Hero Academia 3rd Season follows Izuku Deku Midoriya, an ambitious student training to achieve his dream of becoming a hero similar to his role model—All Might. Being one of the students caught up amidst the chaos of the villain attack, Deku must take a stand with his classmates and fight for their survival.