Saitama vs. Groribas and Geryuganshoop

Saitama vs. Groribas and Geryuganshoop were two battles between the B-Class hero Saitama and the Dark Matter Thieves generals Groribas and Geryuganshoop.

Prelude
Shortly after the S-Class meeting and the Dark Matter Thieves' invasion, Saitama jumps up, crashing through several floors of the headquarters to see the spaceship. The hero decides to go in to investigate and jumps up. Suddenly, a barrage of bullets shoot out of the ship, most of which Saitama manages to easily dodge midair. Then, as another bullet hits him, Saitama stops its trajectory with his foot. The hero states that he's had enough, and tells them to get lost. Saitama kicks the bullet back towards the ship, creating a hole through which Saitama enters.

Battle
Saitama proceeds to navigate through the ship, killing off any shipmates he may encounter. While he is running, a burst of deep laughter is heard throughout the room, causing Saitama to look up. The laughter is revealed to have come from Groribas, one of the Dark Matter Thieves generals. Groribas congratulates Saitama for reaching it this far, but assures him he's reached the end, assuring the hero there is no hope to defeat him. Groribas jumps down to combat Saitama, yelling that his acid spit will melt him away, yet as he prepares to activate his acid spit, Saitama meets him midair and punches the upper portion of his head off, ending his life and making Saitama victorious. While Saitama is running through the ship, he wonders where "the boss man" is and whether or not he's even still alive. Meanwhile, in the control room, Geryuganshoop is nervously analyzing the damage the intruder has caused, and is shocked to see that Groribas is dead. While he is doing this, Boros comes out of his throne room to ask what the problem is. Geryuganshoop replies that he made a terrible mistake and let one of the natives onto the ship, commenting that in just 4 minutes, 23% of the ship has been damaged. Boros assures the psychic that as long as the power core is intact, the ship will remain functional, and he returns to his throne room. As he is walking back, Geryuganshoop informs Boros of the death of Groribas, which mildly surprises Boros, but he ultimately shows no grief towards his death.

As Saitama continues to navigate through the ship, Geryuganshoop uses his telepathic abilities to make contact with Saitama, and warns him not to take another step or else he'll be killed. Saitama tells this voice that even if he wanted to leave, he had no idea where he was. Mildly relieved at the thought of the intruder leaving, Geryuganshoop decides to guide Saitama out and tells him to take a right. To the psychic's shock, instead of going right, Saitama deviously smiles and goes to the left. Geryuganshoop tries to make Saitama go back, but he continues running down the hall with a smile on his face, and within a few seconds, comes bursting through the door. Geryuganshoop, angered at Saitama's flagrant attitude and destruction of the ship, decides to battle Saitama himself and telekinetically throws debris toward Saitama. Declaring himself the top esper in the universe, Geryuganshoop vows to mush Saitama into a bloody pulp. Believing there to be no other option, Geryuganshoop decides to use his Telekinetic Gravitational Wave. Upon hearing this, the crew members immediately attempt to run and escape the attack, but are unsuccessful and instantly crushed by the telekinetic power. Saitama, on the other hand, is completely unfazed by the gravitational technique and scratches his face in boredom and curiosity. Geryuganshoop, once again enraged, decides to use another one of his special moves and begins collecting nearby rubble, spinning it around at amazing speeds, and hurls all of the small debris at Saitama. The psychic believes he has achieved victory, but he is quickly proven wrong, as Saitama remains standing there uninjured. The bald hero remarks that tossing pebbles around was a waste of psychic powers since anyone can do that. He observes a small rock, and chucks it at Geryuganshoop's head, splitting it in half and ending the alien's life, making Saitama the victor.

Aftermath
Saitama is unharmed and asks for directions to Boros' throne room. He eventually ventures to the throne room where Boros waits, which leads to the final battle between the two.

Trivia

 * The fight between Saitama and Geryuganshoop takes place in the throne room in the manga but in the control room in the anime.