The following contains spoilers for One-Punch Man Chapter 166, "The Awakening of the Gods," by One, Yusuke Murata, John Werry and James Gaubatz, available in English via Viz Media.
One-Punch Man may be a manga featuring superhumans redefining human limits, but it mostly pokes fun at common tropes than it adapts them. The manga enjoys building up tension only to have its main character anticlimactically end the fight. Interestingly, its most recent and arguably most hyped battle yet -- the match-up between Saitama and Garo -- veers off from One-Punch Man's usual storytelling. At least, that is what it initially seemed.
Garo and Saitama's fight has literally undergone multiple ups and downs. Just like in all his previous matches, Saitama didn't take Garo seriously at first. Even having the gall to mock the Hero Hunter as he received the latter's attacks. Garo also reached the point of acknowledging the unbridgeable gap between them until a God appeared and granted him divine power. Garo used said power to reach a level even he never imagined reaching. Since the divine power allowed Garo to execute nuclear attacks and copy other characters' skills, he went on a senseless rampage to realize his dream of being the symbol of fear.
The mere radiation the Hero Hunter emitted caused even the strongest heroes to collapse, hence, his existence posed a threat to Earth. The latest chapter revealed that these characters not only collapsed, they lost their lives, as evidenced by Tareo's death. To reverse this catastrophic event, One-Punch Man uses takes same path as Avengers: Endgame.
In Avengers: Endgame, Thanos had already successfully eradicated half of Earth's population, including some of the Earth's mightiest superheroes. The Avengers had to return to different periods in the past and retrieve the Infinity Stones. After which, they faced the past version of their ultimate nemesis and defeated him, thus reversing the mass murder future Thanos committed and finally returning the situation back to what it used to be.
Though One-Punch Man's version of events is more tame, the results are undeniably similar to Endgame. After Saitama beat Garo to submission, Garo finally returned to his human self. He finally recognized the unbridgeable gap between him and Saitama, as well as the reckless futility of his actions. As such, he asks Saitama for a favor. He made Saitama copy and master his skills, obtaining a God's power without the need to borrow it. However, such an act alarmed the God who bestowed his divine powers. Said God revoked Garo's divine power, resulting in the Hero Hunter suffering the same fate as future Thanos.
Before Garo perished, Saitama managed to master the villain's ultimate skill -- time travel. Time started to flow backward. Saitama was quick on the uptake and realized what was happening. He went back to when Garo first appeared in front of the heroes and gave him an unavoidable punch, successfully defeating him. By doing so, Saitama reversed an ominous future where most of One-Punch Man 's cast died and saved all of them, including his beloved disciple.