One spring break, Araragi Koyomi was attacked and bitten by a vampire. He was saved by a strange old man named Oshino Meme who helped him regain his humanity, although Koyomi still has lingering abilities like superhuman healing.

Now Koyomi can’t help but notice how mysterious his reclusive classmate Senjougahara Hitagi is. One day, he discovers the secret of her body when he saves her and finds she is unnaturally weightless. Hitagi violently threatens him to forget her secret, even stapling the inside of his mouth, but Koyomi knows he needs Oshino’s help once more -- this time to help Hitagi. But in a world everyone has a monster inside them, is there ever getting rid of the darkness within?