Behind the city center, 100 meters underground where law and ethics have evaporated, lies the circular arena 'Gehenna.'

Wealthy elites in ultra-luxurious VIP seats watch through bulletproof glass as a single human gladiator is deployed, followed by a swarm of ferocious beasts captured from otherworldly rifts. They bet tens of billions on the gruesome sight of humans being torn apart.

The only weapons allowed in the cage are a single dagger or bare hands. However, two monsters reign over that hellish slaughterhouse: Guest and Yoo Chan.

For these two top predators, who felt a profound boredom toward the weak humans of the outside world who break at a touch, this place is the best hunting ground they found themselves and their only playground that makes their blood boil.

Even the organizers cannot dare to control them, serving them like masters by offering astronomical fight money, freedom to go out, and separate private rooms on the top floor, yet they constantly gather strong monsters in hopes of killing them.