Warning! Spoilers for One-Punch Man chapter 148 ahead!
After a months-long break, the One-Punch Man manga returns to the battle between the S-class heroes and the Monster Association's remaining elites. The deteriorating situation is a good reminder of just how far some of these characters like Genos have come thanks to the influence of mentor Saitama.
While the majority of the latest chapter deals with Bang and Garou as master and pupil battle it out, chapter 148 takes a moment to check in with Genos and Tatsumaki (Aka Tornado), who haven't been fairing well. After pushing herself to the limit to defeat the Monster Association's secret leader Psychos, Tatsumaki has been rendered helpless, becoming an easy target for the competing monsters. Genos has been trying to come to her aid, but his attempts haven't fared well; faced with the hive-mind army of the disgusting Black Sperm, he's literally being torn limb from limb, and yet Genos' nearly helpless body continues to try to protect his exhausted comrade.
Genos' behavior here definitely marks a strong contrast with his first appearances in the series. In his initial fight against Mosquito Girl, the risk of losing prompted him to attempt to self-destruct, under the impression that it was more important to take this monster with him no matter the collateral damage. Faced with a losing situation now, however, Genos decides that it's more important to protect Tatsumaki than destroy the monsters at the cost of both their lives—a marked change in the cyborg's understanding of how a hero behaves. In the moment, he may be inspired by Fubuki's efforts to stop his core overload a few chapters earlier, which required her to put herself at risk to do something she wasn't even sure would work. Repaying that favor by protecting her sister seems only logical, in that regard.
However, there's more to it than simply repaying a favor, as Genos himself notes in the moment. This decision represents a major change in his thinking, as he's not only valuing the lives others more highly, but also his own. If Fubuki (AKA Blizzard) was willing to risk herself for his sake, then that's a clear indicator that his life has value beyond his ability to defeat monsters. The Genos who first appeared thought of himself as little more than a weapon to defeat evil, but spending time with Saitama and the others has shown that he has more to offer than that. And yet, that realization hasn't led to any narcissism on his part; instead, he's willing to submit to some pretty horrible suffering caused by those monsters on the chance that both he and Tatsumaki can still survive. The difference in his behavior couldn't be more radical, and it's ultimately thanks to Saitama's influence that Genos has been able to grow this far.
The battle with the Monster Association has truly been a brutal conflict, and the heroes have suffered more than their fair share of losses at this point. While Saitama has disappeared from the battlefield for the moment, he's still having a positive impact on the fight's outcome simply from what he's taught to Genos and the others... even if it was largely unknowingly. Genos, like the fans, is certainly hoping that One-Punch Man himself will show up soon to save the day, and what that means is that (for now) their goal must be survival.