Koyomi Araragi has recently survived a vampire attack and encountered several girls tormented by supernatural entities. Amidst all this, he wakes up one morning to discover he has been kidnapped and bound by his girlfriend, Hitagi Senjougahara. Araragi's sister, Karen, has crossed paths with Deishuu Kaiki, a swindler who previously conned Senjougahara's family. Consequently, Senjougahara has detained Araragi to protect him from the cunning Kaiki. However, upon receiving a frantic message from Karen, Araragi sets out to rescue her. In addition to Karen's troubles, Tsukihi, Araragi's other sister, faces issues of her own. When two mysterious women enter their lives, even Araragi cannot anticipate their true objectives, nor the catastrophic truths about his family that are soon to be revealed.