After time traveling to the past with Shinobu Oshino, Koyomi Araragi meets Mayoi Hachikuji and returns her backpack, which she left in Koyomi's room. That is when they witness something unidentifiable - something that can only be expressed as the "darkness."
Koyomi, instinctively feeling danger, sits Mayoi on his bicycle and attempts to escape, but the ever-elusive "darkness" tries to swallow the two of them. They barely manage to escape with the help of the young shikigami girl, Yotsugi Ononoki, and they evacuate into the ruins of the cram school. There, Shinobu tells him that she encountered the "darkness" about 400 years ago. Then a woman named Izuko Gaen, who says she knows Meme Oshino, explains to them the nature of the "darkness"... and Koyomi has to face Mayoi's tragic fate.
It, like the dark that makes up most of the cosmos, is not an aberration. Nonbeing can swallow you whole, yet if anything, it’s the anti-aberration. Darkness, in fact, is the Law, an executioner from whom a mark can try to run and hide, but only for so long. When it comes calling, the fortunate just might have the time to say goodbye. And the Darkness is—here now.
Before ever visiting Japan to find a place to die, four centuries, indeed, before her failed suicide attempt, the legendary vampire Kissshot literally stepped foot on the land of the rising sun with an epic jump that ended a lonely sojourn in Antarctica. It was back in those days that the proud noble created her first thrall. It was then, too, that she first met the Darkness.
Having messed with a more recent past with her help, and returning to the present to reunite with two more characters that look like little girls but are actually his elders, Thrall No. 2 Araragi reclaims the mic only to cede it in large part to the bloodsucking demon who goes by “Shinobu” these days. Her story, though, may not even be the most poignant one told herein.
