Saitama Introduction Arc

The Saitama Introduction Arc is the first arc in the Introduction Saga, and the very first arc in the series.

Plot
The story begins with the monster Vaccine Man destroying a city, while Saitama watches the event take place on TV, deciding to intervene. As Vaccine Man is about to kill an innocent child, Saitama shows up to save the child and tells Vaccine Man that he is a hero for fun. Vaccine Man transforms, and prepares to fight Saitama, but is killed by Saitama in a single punch. Saitama then gets on the ground proclaiming that he was upset by how easy that was.

We then flashback to when Saitama encountered the monster Crablante, who was after a young child that drew nipples on his shell. Saitama kills Crablante to save the child, and afterwards trains to become a hero. We then flash forward to Saitama shopping for food. However, he is interrupted by the Brain and Brawn Brothers, who he swiftly defeats, but accidentally destroys B-City in the process.

While in his apartment, he is attacked by the Subterraneans who give him his first real fight in 3 years, but as he is about to face off against their leader it is revealed to be just a dream. After the real Subterraneans invade the surface, Saitama instantly kills the Subterranean King, and they retreat.

Story Impact
Arc Introduction
 * This protagonist, Saitama, is introduced along with his frustration at being so overwhelmingly powerful that he almost always wins his fights with a single punch.
 * B-City and D-City are destroyed by Marugori and Saitama.
 * In a later arc, it is revealed that credit for defeating Vaccine Man went to King, who happened to be there at the time.
 * It is revealed that the boy that Saitama saved from Crablante was the grandson of a wealthy man named Agoni, who would later found the Hero Association after the incident.