Monsters from the Monster Association launch simultaneous attacks on all the human cities, attempting to overwhelm the forces of the Hero Association. Meanwhile, the 'Super Fight' martial arts tournament kicks off.
Saitama is a superhero who has trained so hard that his hair has fallen out, and who can overcome any enemy with one punch. However, because he is so strong, he has become bored and frustrated that he wins all of his battles too easily.
One-Punch Man - The Martial Arts Tournament Synopsis and Schedule