Warning: Contains spoilers for One-Punch Man #167
The manga One-Punch Man just made its protagonist Saitama suffer for the first time since the beginning of the series, and it did it in the most unexpected way: by giving Saitama what he always wanted.
Over the course of One-Punch Man, Saitama became one of the most iconic characters in modern manga. Much of the success of the series is due to the uniqueness of the protagonist. Saitama is the complete opposite of the classic shonen hero. He is so strong that nothing and no one poses an actual challenge for him, meaning he does not have to struggle or train to defeat his opponents. This also means that Saitama is constantly bored and uninterested in what is going on around him, which is pretty unusual for the protagonist of a story but made One-Punch Man really stand out in the manga landscape. Saitama's only drive in life is to find a worthy opponent that will make him use his full strength and cast away his boredom. However, when this finally happened, the outcome was not what Saitama expected.
Garou, the Hero Hunter, is the first opponent who is able to fight on par with Saitama, thanks to the power-up received by the mysterious villain called God. Before Saitama could rejoice in having found a worthy opponent, however, Garou killed his best friend and self-proclaimed disciple, Genos (aka Demon Cyborg). This tragedy shook Saitama to the core and made him realize his own shortcomings as a hero. In chapter #167 of One-Punch Man, Saitama realizes he can finally let loose and unleash his full power, but also that the fulfillment of his wish does not make him happy at all. It's an incredible turning point for Saitama and for the series.
Until now, Saitama has been defined by his obliviousness and apathy, no matter what horrible monsters or crazy end-of-the-world scenario he was facing. This was often used for comedic effect in the series, but it also made Saitama a unique kind of protagonist, one that could not be hurt or harmed in any way. Now, for the very first time, the hero of One-Punch Man is actually suffering (emotionally), and it happens right when he has gotten what he wished for. The loss of Genos makes Saitama realize that his pursuit of a strong opponent was, in fact, an empty quest, because it made him forget what it actually means to be a hero: protecting the people and things you care about.
One-Punch Man is forcing Saitama to evolve by experiencing pain for the first time, and by realizing how vain his goals were. It's a tragic but also very compelling moment that puts the protagonist back on his "hero journey", which requires him to suffer to move forward. The series has taken a very interesting turn, proving that One-Punch Man fans should not take Saitama for granted.
You can read One-Punch Man's newest chapter now from Viz Media.