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.

After many years of dormant rest, a hot springs fairy awakens in modern-day Japan. However, while she slept, she took on the appearance of a young girl. She decides to cooperate with the locals whilst trying to regain her powers. (Source: LiveChart)

On her way to her first day of high school, Eri Kumagai is captivated by a girl's singing. Her song is beautiful but ends abruptly when the girl steps on a cat's tail and disrupts the moment. Eri pushes this out of her mind until that same girl rushes into her class late, cat in hand, and claims that the name on the attendance list—Chiharu Yuzuka—is her false name and she is actually called Haru Chitose. Much to Eri's distaste, she cannot escape the eccentric Haru, as the two happen to share the same dormitory room. Haru causes one headache after another, but when she snoops around in Eri's laptop and discovers that she is an online composer, Eri is furious. Haru, enamored by Eri's music, desperately wants to sing with Eri, but Eri is dead set against it. Will the two be able to find common ground?

It is Kyouya Sata's 17th birthday, and it seems Erika Shinohara has forgotten about her beloved boyfriend's important day. Even Erika's best friend, Ayumi Sanda, appears to be unaware as she asks Kyouya to tutor her after school. However, behind the scenes, Erika is preparing a surprise in Kyouya's apartment and has assigned Ayumi the job of distracting him. Not everything goes as planned, though, as in front of Kyouya's home, an unlucky accident sets Erika into a complete frenzy—meaning Kyouya now has to find a way to calm down his oddball girlfriend.