The second season of the Monogatari Series, part 3/3. Contains the arc Yotsugi Doll from the Tsukimonogatari light novel.

Koyomi Araragi is studying hard for his college entrance exams when he notices something strange: his reflection no longer appears in the mirror, a characteristic of a true vampire. Worried about the state of his body, he enlists the help of the human-like doll Yotsugi Ononoki and her master Yozuru Kagenui. Quickly realizing what the problem is, Kagenui gives Araragi two choices: abstain from using the vampiric abilities he received from Shinobu Oshino, or risk losing his humanity for good.

(Source: MAL Rewrite, edited by Edo)