Gameworld is a 2017 short story written by Jonathan Maberry, published by Titan Books as part of the anthology Predator: If It Bleeds. In it, a desperate man seeking funds to treat his daughter's cancer enters a brutal hand-to-hand combat tournament held on a remote asteroid, where men fight both each other and all manner of strange, vicious creatures to the death.
Former champion sumo wrestler-turned-trillionaire businessman Sake Chiba now runs Gameworld, an illicit club established in the asteroid belt between Mars and Jupiter that plays host to a brutal fighting tournament. Open for any to enter, it pits the strongest, most savage men against each other, as well as generically-modified creatures, in savage, unarmed fights to the death, with huge sums of money available to the victor.
When his youngest daughter is diagnosed with cancer — and with the cost of life-saving treatment far exceeding what he can afford — former special forces operative Hogarth Fix enters himself into the tournament on Gameworld, hoping to earn enough to save his daughter's life and ensure she and his other two children are financially secured for the rest of their lives. Night after night Fix waits to be called into the ring, terrified of what he might face, but comforting himself with the knowledge that victory will set his children up for life, while death will mean his life insurance will likewise cover the cost of his daughter's treatment.
While sparring with an opponent in Gameworld's training center, Fix catches Chiba's eye, and is invited to meet with him in his office. Chiba reveals that he knows all about Fix's past and his reasons for entering the competition, and expresses admiration for the obvious skills Fix displayed while sparring. Chiba goes on to offer a deal — Fix will fight a single bout against a special opponent, and should he win, Chiba will pay him a huge sum of money, far beyond what he would require to pay for his daughter's treatment. When Fix cautiously inquires who this special opponent might be, Chiba reveals that it is a captured alien creature, found among the wreckage of its ship on the dwarf planet Ceres. Although none of his men know precisely what it is, its strength and prowess in physical combat have been aptly demonstrated. Reluctant but unable to ignore the potential reward, Fix agrees.
Over the next few weeks, Fix trains relentlessly, and is offered every comfort by Chiba. When fight day finally arrives, the crowed is stunned into a frenzy at the prospect of a brawl between the hideous alien, which Chiba has christened the Nightmare Kid, and its human opponent. The bout begins. Fix quickly learns that the creature is brutally strong and armed with razor-sharp claws, but naïve in its technique. Using his superb knowledge of hand-to-hand fighting, Fix is able to read the creature's movements and avoid any serious damage, while retaliating with surgical strikes against weak spots when he can. Although the fight is savage and closely contested, Fix finally overcomes the Nightmare Kid with misdirection and knocks it down. As he prepares to finish it by breaking its neck, an explosion knocks him to the floor.
A much larger version of the creature Fix had been fighting enters the club through the hole it has blown in one wall and begins massacring the occupants with blades and an energy weapon; Fix realizes that it is likely an adult from the same species as his opponent, who is a mere juvenile. In the chaos and carnage, he sees Chiba flee to his office with the Nightmare Kid in pursuit. Seeing an opportunity to secure the money he needs, Fix follows. When he finally reaches the office, he finds Chiba beating the juvenile creature, its strength failing due to the numerous injuries it has sustained fighting through Chiba's guards. When the adult blasts its way into the room, Chiba pulls a gun and holds it to the Nightmare Kids' head, threatening to kill the juvenile if the adult attacks.
In the midst of the standoff, Fix throws his knife to the Nightmare Kid, which uses it to brutally gut and kill Chiba. In the aftermath, Fix witnesses the adult slapping the juvenile, apparently berating it for its failings, before the younger creature tears out Chiba's skull and spine as a trophy. After briefly acknowledging Fix and thanking him for his intervention, the two creatures depart, leaving Fix alone in Chiba's office, staring at the safe — filled with vast quantities of money — that hangs open in one wall.