Simon's first reign lasts less than two hours. He dies in the explosion that consumes the imperial court, then wakes up to Lauriane shaking him again. He quickly learns that the Overlord Class carries a curse: revealing its secret triggers a failsafe that kills him and resets the loop. He also discovers that levels and perks carry over between reigns, giving him a slow but cumulative advantage. His second death comes when he accidentally hints at time travel, and his third when he is poisoned during a council meeting. Each death teaches him something new about the palace's factions, the assassin's methods, and the limits of his power. He begins to manipulate events by forging his father's testament, naming a fictional heir to buy time, and secretly preparing to escape to the Imperial Military Academy. But the loop is not a simple do-over; the world remembers nothing, and each reign is a fresh chance to make different choices, but also to lose everything he has built.

Simon escapes to the Imperial Military Academy in Telluria, hoping to level up and avoid the civil war brewing at home. There he befriends his childhood friend Anna Paimon and a charismatic student named Casval, who shares his interest in the ancient Kish Empire's treasures. But Casval is not what he seems. When Simon and Anna invite him to a private party, Casval murders Anna and then reveals himself to be a dragon in human form, a child of the former Overlord Gargauth. Simon dies again, but not before learning that the conspiracy against House Magnos is far larger than he imagined. In subsequent reigns, he sets a trap for Casval, luring him into a confrontation with Thalas that ends with the dragon prince devoured by his own sister, Vouivre. Simon now knows his enemies: a dragon warlord bent on reclaiming the Crimson Throne, and a shadowy organization that may have killed his father.

After being legitimized and betrothed to Anna, Simon travels to the Berwick Islands to build a power base. There he discovers a hidden dungeon beneath Castle Carcas, the Poison Gardens, and a voice calling him from the depths. He ventures down with his retainers only to encounter a creature of unimaginable power: the Berwick Lich, who introduces himself as Elios Magnos, Simon's own ancestor and the creator of the Crimson Throne's cycle. The lich kills Simon's retainers with a mere thought and reveals that the dungeon contains a sealed Zodiac Fiend, one of twelve archdemons imprisoned since the Age of Heroes. He warns Simon that the fiends will awaken when a black comet returns, and that Simon has only ninety reigns left before the cycle ends. Simon escapes with his life but loses his loyal knights. He now understands that the Overlord's curse is tied to an ancient cosmic war, and that his father's obsession with astronomy was a desperate attempt to prepare for the coming apocalypse.

Realizing he cannot stop the civil war or the dragon conspiracy alone, Simon frees the elven slave Belzemine and the Kish songstress Eole, then flees the empire for the western continent. He joins an adventurer guild in Valne, hoping to gain experience and resources, but his true identity is betrayed by the criminal syndicate the Cobweb. The Paladin, Ser Alphonse of Lore, ambushes him on a mountain summit with a company of elven mages. Simon fights Alphonse in single combat and kills him, but the elves seal him in stone for what feels like decades. He awakens to a world in ruins: a black comet hangs in the sky, demons and dragons battle over a burning landscape, and Vouivre has enslaved Eole. Simon is stabbed in the back and dies, but not before learning that his hidden Serpent-Bearer perk activated when the comet appeared. He now knows that his reign count is running out and that the apocalypse is coming.