Saitama, who appears uninteresting, has a somewhat unusual hobby: he is a hero. Saitama fiercely trained for three years to fulfill his boyhood passion, losing all of his hair in the process. Saitama is now so powerful that he can defeat any foe with a single punch. However, the fact that no one can equal his might has caused Saitama to face an unforeseen problem: he is no longer able to enjoy the excitement of battle and has grown very bored.