Saitama vs. Vaccine Man

Saitama vs. Vaccine Man is the battle between the amateur hero Saitama and the Dragon-level Monster Vaccine Man.

Prelude
Vaccine Man arrives and attacks A-City, using Energy Balls to destroy the nearby buildings. The Hero Association send out Smile Man and Lightning Max, but they were easily defeated. Saitama sees the news report and decides to go out and save the day.

Battle
Vaccine Man attempts to kill a little girl, but Saitama saves the child. Vaccine Man asks for Saitama to identify himself and he does, by saying that he's just an average man acting as an average hero. Vaccine Man is angered by this and aggressively tells the tale of who he is and where he came from. Vaccine Man then began transforming into a giant monstrosity and tells Saitama about his origins. As Vaccine Man is about to attack, Saitama simply punches him, killing him.

Aftermath
After Saitama defeats Vaccine Man, he is seen pounding his fist in anger because of the lack of a challenge he faces. Credit for defeating Vaccine Man went to King, who happened to be there at the time.

Trivia

 * The battle lasted 21 seconds.