The Villain of the Octagon

Shin Chi-beom, a talentless amateur mixed martial artist, returns after vanishing for a week and kills his opponent in the cage, leaving everyone wondering what has changed. During his disappearance, Chi-beom wakes in ancient Greece as a combat slave forced to fight in the deadly Pankration. He endures five years of life-or-death duels, fighting dozens of times a day, before returning to his original body after the final battle. Left with severe trauma and mental illness, he finds peace only inside the cold, octagonal cage, where he keeps searching for the strongest. Can he find rest when the fighting ends?