Office worker Satou Konoha dies in an accident and is reborn as a character from a story she wrote as a student—The Dark History. Instead of reincarnating as the heroine as she'd hoped, she's the hated little sister, Iana. And, according to the story, she's destined to perish early on at the hands of her butler! There's only one way to survive—remember the plot of the story and avoid her fate!

To save Konoha from the monster that kidnaps her, Iana triggers her own death flag. With help from Sol, Ginoford, and the others, Konoha's rescue succeeds. Iana barely has time to relax before an invitation to a ball arrives from the capital—the very ball that's the setting for chapter 3 of The Dark History. If Konoha dances with the prince at the ball, it will lead to a death flag for Iana!

As Iana grows used to life in the world she's been reincarnated into, a young man comes to visit—her childhood friend Yomi, back from studying abroad. When Iana remembers Yomi, a character she created, she is left aghast. His role in the novel is to kill Konoha. If he acts according to the story, it will lead to Iana's death. Iana tries to convince Yomi to stop, but it only makes things worse.

Yomi mistakenly believes that Sol is tyrannizing Iana. His pure love and loyalty to Iana lead him to target Sol's life. He sets up a magic trap, creating a man-eating flower that attacks Konoha. Ginoford and Sol defeat the creature, but Sol believes that he's the target of the strange events that have occurred, including this attack, and he turns to Iana with a gaze full of suspicion.

Iana confronts Yomi, taking up Sol's sword in his place, but it's so heavy that Iana can't even swing it. Yomi, who loves Iana, concedes the duel, casting his own sword aside. The matter is settled for the moment, but if nothing changes Yomi will keep trying to kill Konoha. No amount of persuasion from Iana seems likely to make Yomi give up. What desperate measures has Iana come up with instead?

Iana sneaks into town with Konoha where she sees just how popular Konoha is, and how despised she is herself. Back at home, a man named Cheneau drops by. He's vice captain of the Police Security Force's Hydrangea Unit, and he once arrested Iana on suspicion of Konoha's attempted murder. He's been investigating the disappearances of beautiful young ladies, and he has his eye on Iana as a suspect.

Iana heatedly declares to her new friend Menoa's older half-sister, "This girl is no slave!" By causing an uproar at Duchess Amaryllis' party, Iana attracts even more suspicion from Cheneau. And right at that moment, Menoa disappears. Iana, who found and picked up the earring that Menoa was wearing, is suspected to be the culprit behind the disappearing beauties incidents.

Duchess Amaryllis is Bloody Rosa, the person who has been kidnapping beautiful girls. In order to save Menoa, Iana convinces Cheneau to help her, and they commence working together. But a trap sends Iana and Cheneau tumbling into Duchess Amaryllis' hands. The two are held captive in the basement—an insane "paradise" where the kidnapped Menoa and Cheneau's younger sister are also being held.

To save Cheneau, Menoa, and the abducted beauties, Iana confronts Duchess Amaryllis as the brilliant villainess, Iana Magnolia! The Hydrangea unit arrives just in time, but Iana realizes that the captured duchess is resolved to die and acts to save her. The case is closed. Or, it should have been, but for some reason, Sol is enraged. Has this incident flipped his murderous motivation switch?

Iana has fought hard to change the Dark History, but she realizes that the story is being altered in ways that she can't control. While visiting a country villa, Iana and the others meet a boy accompanying a wounded elf and decide to look after them—an event that signals that the vampire incident is about to occur. As Iana prepares to check the vampire's tomb, Sol asks her to take him along.

The seal on the stone tomb is broken. As Iana races to look for the one who is missing from the coffin, she is attacked by elves who have turned into vampires. Sol and Yomi come running and save her, and after realizing that she isn't alone, Iana continues onward. But when Shukuna appears to help them, he guides them to a place where an unexpected twist awaits.

Iana attends upon the Vampire King, but it's all an act. Traces of Konoha's saintess blood on her handkerchief allow Iana to escape being turned into a vampire, and she challenges the Vampire King to battle, alone. Then, when she goes back to find Yomi, she discovers that there has been an unexpected turn of events. What is happening in the pages of the Dark History?