The Strongest Man
Saitama is a guy who's a hero for fun. After saving a child from certain death, he decided to become a hero and trained hard for three years.
The Deep Sea King
Saitama and Genos head to the shores of City J to stop a pack of monsters calling themselves the "Clan of the Seafolk".
Saitama tags along to an emergency meeting of Class S heroes and discovers that a seer has foretold a serious danger threatening the Earth.
The Dominator of the Universe
As a colossal spaceship floats in the skies above City A, a member of its monstrous crew battles on the ground against a group of S Class heroes.