Set two months after the events of Corpse Party: Book of Shadows, Ayumi Shinozaki had paid the price for her use of black magic and been afflicted with a serious illness. However, she managed to somehow survive with the help of Naomi Nakashima. The grim grimoire, known as the Book of Shadows, now has laid waste to the Shinozaki estate and both the estate and tome vanished, leaving only a plot of land where it once stood.

Before she was hospitalized, an acquaintance of Ayumi's older sister, Hinoe Shinozaki, who belongs to the W.I., the Wiccan Institute, an organization that worshiped spirits. Telling Ayumi to get Book of Shadows back, her trail now leads into the residence once belonged to Makina Shinozaki.

The day after being discharged from the hospital, Ayumi went to visit the estate where Makina Shinozaki resided. However, it was run-down and looked to have been closed for a long time; "NO TRESPASSING" tape was strewn up everywhere, blocking entry. She stared intently at the estate with fierce determination. ...She couldn't afford to let Satoshi and the others be involved this time. For Ayumi, it was the responsibility of Shinozaki's bloodline. The lone struggle and legacy of her lineage.

[Edited from Corpse Party Wikia]