Guest, an ordinary unemployed person, reincarnates one day as the final villain of a martial arts novel: the Leader of the Demonic Cult.

In the original story, the Demonic Cult Leader commits countless atrocities before being subjugated by the Righteous Faction and the Murim Alliance, eventually meeting death by decapitation at the hands of the greatest Sword Venerable, Mukyeon. Knowing this ending, Guest tries to stop the senseless slaughter and change the original tragedy to survive. However, the world already regards Guest as the greatest villain under heaven, and no one believes in this change.

In particular, Mukyeon—the one who kills Guest in the original work—is a man who lost everything to the Demonic Cult as a child and hates them intensely. Even if Guest performs acts of kindness, he views them all as schemes and never trusts them. He does not feel gratitude even if Guest saves his life, believing that killing Guest is his sole mission.

Guest cannot kill Mukyeon to change fate, and Mukyeon endlessly seeks to kill Guest. The two, who hate each other most, are entangled in the worst ill-fated relationship with no trust or compromise—a destiny that must end with one person cutting down the other.