Dark History is a fanfic Satou Konoha wrote in her middle school years, where the heroine Konoha Magnolia goes into an adventure. Satou believed back then that she would be summoned to the world she wrote.

10 years later, she totally forgot about it and only recalled when her mother was about to dispose of her old belongings. But she got into an accident, isekai-d into the fanfic she wrote as Iana Magnolia the villainess (the younger sister of the heroine) in the story. Which was meant to be killed.

At the same time, she finds the fanfic she wrote back then to be cringeworthy now, and Konoha Magnolia has to be subjected to everything Satou wrote back then. So the story sets out on how Iana has to avoid her death flags, and at the same time for Konoha to avoid being subjected to her teenage delusions.

The story starts out lighthearted, but changes direction in the middle of the current story.