
The two set out to conquer the world, only for the older brother to observe, in shock, that Saitama is riding on his brother's other shoulder. The man is the result of an experimental steroid called " Biceps Brachii King" developed by his mad scientist older brother. As present-day Saitama reminisces about the events while shopping, a colossal man attacks the city. When Crablante finds them, Saitama decides to protect the child, and kills the monster by ripping out its eyestalk with his necktie. Saitama promptly encounters the child, who is revealed to have drawn nipples on Crablante with a permanent marker while he was asleep. The monster spares him, explaining that it is hunting a boy with a large chin. The episode then switches to a flashback three years before he became a hero, showing an unemployed Saitama's encounter with Crablante, a man who gained crab-like features after eating too much crab. After a single punch killed the monster, Saitama screamed in frustration. Vaccine Man then transforms himself into a giant monstrosity and Saitama destroys him with a single punch.

The monster introduces itself as Vaccine Man and claims to have come into existence to eradicate mankind due to their pollution of Earth. As the monster is about to kill a girl, an incoming Saitama arrives and saves her. A reporter tells what has happened and then the report was suddenly cut out and a bald man named Saitama decides to leave.


A monster appears in A-City and begins to wreak havoc as he defeats Lightning Max and Smile Man.
