Warning: contains spoilers for One-Punch Man chapter 165!
The latest chapter of One-Punch Man released in Japan, chapter 165, has taken the battle between Saitama and Garou in a radically new direction, taking the hero hunter who was so close to redemption back to villainy in a bizarrely tragic way: finding God.
One-Punch Man's God is a mysterious figure. It's known to have a grudge against humanity, and has lent its power to many a monster, including the recently defeated Homeless Emperor, who had his divine powers repossessed at the cost of his life after failing. It lures people into making contracts with it, often through the use of mystery cubes that are extremely heavy and which automatically draw its attention to the cube's holder. Flashy Flash and Saitama found one of these cubes, but were kept from accidentally forming a contract by the Number One hero, Blast. Afterward, it also tried to trick Tatsumaki into taking its hand, using the guise of Blast to try to win her trust, but she saw through the illusion. No matter what it tried, God just wasn't able to trick the heroes.
Garou, on the other hand, was both desperate for more power and eager to stand against the heroes, making him a perfect target. Taking on the appearance of his former master, Bang, God reached out to Garou, and Garou began to reach back before recoiling, realizing this was an out-of-character moment for Bang, but it was too late. Garou's hand touched God's for an instant, and that was enough. God openly stated his intention to use Garou as a puppet, and while Garou has since insisted that he's operating of his own free will, that hardly means he isn't still doing as God wants. His monster armor and all detail on his face have been replaced by a void of stars and galaxies, much like the void God first appeared in, which (visually) suggests that there might be a lot less of the real Garou left than thought.
Garou had previously taunted fate and declared himself the next god, which may have been part of what drew God's attention to him, but he's hardly been the first to make such a claim. The incredibly huge centipede monster Centisennin referred to a being that Garou now believes to be Saitama as "the abominable fist that stands against God," suggesting that God is quite worried about Saitama and his growing power, as he represents a threat to its plans for the extinction of humanity. In retrospect, it seems likely that the wave after wave of horrible incidents, from the meteor impact in City Z to the Monster Association itself, have all been part of this evil God's efforts to wipe out human civilization.
Garou's desperation to best Saitama has led him to become a pawn, a fate that's particularly tragic given the original version of chapter 164, which saw Garou sitting down peacefully to talk with Saitama over tea. Had God not intervened to prey upon Garou in his weakest moment, One-Punch Man's most anticipated fight may well have ended with these two rivals becoming friends, but now there's no telling what may be left of Garou at the end - if there's even much left now.