Kouji Mikagami is an ordinary high school student whose only standout trait is his exceptional skill at video games. One day he is summoned to the religious nation of Bumbledore, a rigid class society where a person's worth is determined by the strength of their innate skill, or special ability. The summoner, the powerful high priestess Zayd, initially expects to gain a new soldier for the nation's war against a neighboring country. When Kouji's granted skill is revealed to be Copy, the ability to temporarily mimic another person's power at a reduced effectiveness, Zayd dismisses it as a worthless trash skill and immediately has him thrown into the coliseum as a gladiator slave. The coliseum operates on brutal rules: losers become the property of winners and are subjected to forced breeding, enforced by special drugs.

Imprisoned and facing certain death, Kouji meets a fellow slave named Zule, who explains the world's mechanics and the coliseum's rules. Recognizing that the situation is fundamentally a game with defined parameters and win conditions, Kouji resolves to treat it as one. He decides to survive, rise through the ranks, and eventually exact revenge on Zayd for discarding him so casually. His Copy skill, dismissed as the weakest possible ability, becomes his key tool. By observing and duplicating his opponents' powers and combining them with his own gaming instincts and tactical thinking, he begins to win against seemingly impossible odds.

The first major narrative arc involves Kouji systematically defeating Zayd's top four gladiators, known as the Four Flawed Kings or the Four Heavenly Kings. These opponents are all powerful women with distinct abilities and personalities: the flame-wielding knight Mary Landlott, the physically overwhelming martial artist Marle Baroque, the spatial-exchange user Alice Cotton, and Fine Catastrophe, a genius who commands over one hundred different skills. Each battle forces Kouji to devise creative strategies on the fly, using his copied abilities in unconventional ways. After each victory, the defeated opponent becomes his property, gradually forming a group of former enemies who now serve him. The story includes explicit sexual content as part of the coliseum's reward system, with Kouji engaging in intimate encounters with his new slaves.

Following the defeat of the four kings, the narrative shifts into a second major arc centered on tag-team matches organized by Desmos Salamandis, a giant of the ruling class who oversees the coliseum's operations. Kouji must partner with his acquired slaves in two-versus-two battles, adding a layer of teamwork and coordination to his solo strategic approach. Opponents in this arc include the swordsman Musashi and the ninja Suzu, each with their own skills and histories. The tag-team matches explore the backstories of Kouji's allies, particularly Marle's obsessive drive for strength and the hidden past of the fighter Vivian, whose fighting style mirrors Kouji's own. The arc also deepens the political intrigue of Bumbledore and the coliseum's role as a tool of control for the ruling elite. The story remains ongoing, with Kouji continuing to climb the coliseum ranks while managing his growing harem and pursuing his ultimate goal of revenge against Zayd.