Futaro has led five quintuplets to the point where they can graduate and pursue their own dreams. Now, finally, they had reached their final school festival. Having decided to make this occasion one to remember, Futaro searches for his feelings for the five quintuplets.

In Edo period Japan (1603 to 1868), a strange new disease called the Redface Pox has begun to prey on the country's men. Within eighty years of the first outbreak, the male population has fallen to a quarter of the total female population. Women have taken on all the roles traditionally granted to men, even that of the Shogun. The men, precious providers of life, are carefully protected and the most beautiful of the men are sent to serve in the Shogun's Inner Chambers.

The Sacred Kingdom has enjoyed a great many years without war thanks to a colossal wall constructed after a historic tragedy. They understand best how fragile peace can be. When the terrible demon Jaldabaoth takes to the field at the head of a united army of monstrous tribes, the Sacred Kingdom's leaders know their defenses are not enough. With the very existence of the country at stake, the pious have no choice but to seek help wherever they can get it, even if it means breaking taboo and parlaying with the undead king of the Nation of Darkness!

The seemingly ordinary and unimpressive Saitama has a rather unique hobby: being a hero. In order to pursue his childhood dream, he trained relentlessly for three years—and lost all of his hair in the process. Now, Saitama is incredibly powerful, so much so that no enemy is able to defeat him in battle. In fact, all it takes to defeat evildoers with just one punch has led to an unexpected problem—he is no longer able to enjoy the thrill of battling and has become quite bored. This all changes with the arrival of Genos, a 19-year-old cyborg, who wishes to be Saitama's disciple after seeing what he is capable of. 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, and Saitama, shocked that no one knows who he is, quickly agrees. And thus begins the story of One Punch Man, an action-comedy that follows an eccentric individual who longs to fight strong enemies that can hopefully give him the excitement he once felt and just maybe, he'll become popular in the process. [Written by MAL Rewrite]