Saitama and Garou crashed into a celestial satellite, revealed to be Io, one of Jupiter's moons. The two were initially bewildered and confused, but after figuring out their location, Saitama stood above Garou atop a small hill and proclaimed that he could finally let loose against someone who could withstand his full power. Yet, despite that fact, he still didn't feel the least bit excited to finally go all out.
Garou, still annoyed with the current location, suggested that they should find a way to get back to Earth. But Saitama instantly shut him down and said that they would need to figure it out after he defeated him, stating that he only needed one hand to do so.
Unfazed, Garou initiated the fight once more by simply summoning a portal beneath Saitama, only for the caped hero to casually kick it away, much to Garou's surprise. Then suddenly, in an instant, Garou was rocked by a punch from Saitama, sending him flying off the moon. Garou quickly created a portal that brought him back to Saitama and attempted to counter with a punch, only for Saitama to flip Garou's portal upside down, thus making Garou hit the air instead, before he was thumped by yet another punch that sent him rocketing into the floor.
Unimpressed, Saitama told Garou to stop using his cosmic tricks and fight him with his fists, going on to taunt him, asking if these attacks were a so-called ultimate martial art. Garou, offended by his taunt, obliged, saying that he had absorbed countless martial arts and techniques, before he dashed around Saitama with immense speed through multiple portals in an attempt to disorientate him.
He first attacked him with Roaring Aura Sky-Ripping Fist, then deflected a punch from Saitama with Water Stream Rock Smashing Fist, before sending the hero flying with Exploding Heart Release Fist followed by Whirlwind Iron Cutting Fist, then finally ending the combo with Nuclear Fission Gravity Knuckle, which created a massive atomic explosion that was then absorbed into a singularity by the Gravity Knuckle.
Standing amidst the smoke, Garou declared that his fists were unavoidable and that timing was irrelevant regarding his attacks. But to his shock, Saitama once again emerged completely unscathed, save for being completely naked this time, as his costume had been utterly destroyed by Garou's attacks. And as he stood there, he replied to the hunter that he could do something very similar.
The bald king demonstrated this by digging his fingers into the ground with one hand — with one hand — and unleashed a new attack called Serious Table Flip, flipping massive amounts of the moon's crust thousands of metres up into the air, taking Garou with it. The attack then utterly decimated the entirety of the moon itself, unravelling it like an orange peel, all while Garou aimlessly and helplessly hurtled high into the air amongst the innumerable debris.
Suddenly, Saitama dashed around Garou with incredible speed, creating hundreds of afterimages in the process, before he directed his afterimages and himself towards Garou simultaneously with another serious technique, called Omnidirectional Serious Punch. Garou instantly avoided the attack by jumping into a portal, only to see, much to his horror, that Saitama was already directly below him, within the very portal he had just opened, and proceeded to punch him with a Serious Punch.
As the hit landed, it sent Garou flying and ricocheting off the slabs of stone, only for Saitama to follow up once again and punch him away as he was about to hit another slab. Saitama dashed around Garou back and forth with immeasurable speed while punching him across the entirety of the demolished surface of the moon, creating a full-on geometric surface of light from the intensity of the attacks.
Garou then furiously repelled Saitama's flurry of attacks with his Water Stream Rock Smashing Fist and landed on a large slab of debris. Garou attempted to regain his composure while needing to find a way to get above the rocks. He created a portal, only to have his head smash into another slab of rock. Stunned, Garou realized that Saitama's attack had completely warped his sense of direction. And now he utterly felt like a caged insect being played with by a child.
Before he could react, he was suddenly attacked by another Serious Punch from Saitama. Garou was aghast at Saitama's limitless strength, but remained steadfast and declared that if he was to win against him, then he would need to continuously replicate his power and technique until he achieved victory.
As he did this, he once again entered Mode Saitama, before he and the caped baldy both punched each other directly in the face. The battle continued as Garou threw a punch through a hyperspace portal that reached Saitama on the other end, only for Saitama to quickly retaliate with a punch of his own. Instantly, as he was sent hurtling backwards from Saitama's punch, Garou created another portal behind him that redirected him behind Saitama, and used his momentum to unleash an axe kick onto Saitama's head, only for the latter to simultaneously counter with a punch to Garou's guts.
The punch sent Garou back into the portal, with the hero hunter then opening another portal and swiping back at Saitama, only to miss as the bald king jumped backwards. He landed onto a large slab of debris, then leapt downwards with such an immense force that it destroyed the slab, and followed with a monstrous karate chop straight to Garou's neck, which in turn devastated the surrounding area.
The fight escalated as they moved and dashed about the decimated moon in an exchange of vicious blows. Garou was bewildered at the fact that, despite countering him with just as much power, Saitama simply responded with even greater force than before — and still with just one hand — as Garou performed a powerful punch to Saitama's gut.
The latter didn't flinch, and countered with an uppercut that sent Garou flying into the air. It was then explained through the shocked Garou that Saitama's growth in power and strength continuously rose at an exponential rate, with his own strength struggling to keep up, leading him to realize that at this rate he could actually die from one of Saitama's punches. Saitama's strength soared due to an upsurge of emotion from Garou trying to kill Genos earlier.
Garou, now slowly falling behind, dashed around with incredible speed, preparing for an attack. Saitama, meanwhile, only realized that his costume had been completely blown off, and that it had actually started to get cold. An enraged Garou attempted to throw a punch at Saitama, but the bald king casually grabbed it without even looking.
Due to the cold, Saitama was about to sneeze, which forced Garou to instinctively evade. And honestly, he was lucky he chose to, as Saitama unleashed a serious sneeze that not only parted a large portion of the moon's floating debris, but also utterly annihilated and cleared an enormous mass of Jupiter's atmosphere and weather system, revealing the small, supposedly solid surface of the planet. The display of power left Garou in shock.
All the while, they rocketed away from the moon and Jupiter due to the force of Saitama's sneeze. As they soared through space, Garou noticed the sun. Then, using his enhanced vision and perception, he was able to make out a clear view of the Earth, which allowed him to teleport there. Just before doing so, in an attempt to escape, he threw a Nuclear Fission punch directly at Saitama, giving him the opportunity to escape and finally return to Earth via his portal.
After escaping, Garou celebrated his return and presumed victory, only to instantly discover, to his horror, that Saitama was already right behind him, complimenting his last move. Bewildered, Garou questioned Saitama on how he had managed to return, to which Saitama replied by saying that the coldness of space had given him such a stomach ache. And while he had initially been holding it in, Garou's last attack had surprised him and sent him blasting straight back through Garou's portal.