mangaman

There are a few battles in which he has to use more than one punch, but in each of those it is hinted that he is holding back and not being serious. In one battle he is facing an enemy named Garou that seemingly has the ability to grow in power with every defeat until he is stronger than all of the present S-Class super heroes combined, and indeed he does survive quite a few punches during his fight with Saitama(a.k.a Caped Baldy a.k.a Onepunch Man), but no matter how powerful he grows Saitama just gets more serious until it becomes obvious that there is no way Garou will ever become strong enough to defeat him. Basically he isn't just as strong as he needs to be. He is soul-crushingly stronger with absolutely no weaknesses. Renobjc makes a pretty good case and I like the take on Saitama representing God/Budha, but allow me to simplify it a little more. Onepunch Man is ONE's(the web comic's author) critique on battle manga in Japan, where the main characters constantly face ever increasing threats so that they must surpass their current limits in order to win. Saitama has surpassed all limits. He would defeat Superman because Superman has be shown to be beatable.He would defeat the Hulk for the same reason. Who knows who would win if he came up against another unbeatable opponent, but even if he easily managed to defeat everyone on that list nobody would believe he did it. Such is his curse. To never find an opponent he can't easily defeat, and never receiving the credit for doing it either.