Boros is the chief of the Dark Matter Thieves, a team of Alien invaders.
They are responsible for the destruction of A City.
In One-Punch Man, Boros comes to Earth because he is looking for a good fight.
The seer tells him that he’ll find one on a planet far away.
An alien seer capable of seeing such visions and foreseeing a good fight on Earth. He couldn’t have failed to see Saitama.
So, Boros traveled through the universe and destroyed the planets he came across. Until one day he reached Earth and met Saitama.
Saitama vs Boros was the highlight of One Punch Man Season 1.

Saitama is the protagonist of the series One Punch Man.
As the name suggests he is a super character who can crush his enemies with just one punch.
It may sound a little strange at first, and some people may feel that they will eventually get bored, but this is not the case.
Although he is extremely powerful, he still wants to be recognized by people as well as other characters who kept the plot interesting.
Saitama vs Boros
Boros like Saitama never fought anyone stronger than him.
But unlike him, Saitama was bored but never once misused his strength.
Due to his self-healing and highly regenerative powers, he could fight for a long time.
Saitama also after knowing the wish of Boros didn’t finish him with just one punch.
He held back his power a lot and delivered consecutive blows. Saitama did this to let Boros feel excited after a lot of years.

Saitama vs Boros was an absolute spectacle to watch. But it also becomes a difficult disappointment for the Saitama lifestyle.
When Saitama defeats Boros, he begins to complain less about his overwhelming power.
After winning the so-called, “ruler of the universe” in the battle. Saitama seems to have accepted the fact that he will never get a good fight.
Because he no longer says “he had his hopes” towards the end of the whole series.
I think this seems to be a crucial step in the gradual characterization of Saitama.
His dream of fighting on equal terms completely collapses, but at the same time, he begins to grow as a hero.
Now he gets called a professional hero and he is not having fun.
Saitama begins to do his job more efficiently and prioritizes the lives of others instead of his own entertainment.
Like his growing concern for collateral damage, which he did not take into account at the beginning of the story.
His powers have begun to be more positive as he realizes that heroes are meant to save people and are not just cool.
Although the fight was easy for him to win with little effort.
He had never encountered anything as powerful as Boros, so he might have killed him very easily.
He knew that Boros was not just a random monster on the streets and that if he was not there to get him to stop, he could easily destroy the earth.
This realization made Saitama grow as a hero further.

Thanks for reading!