Karen is badly ill, having been poisoned by an evil, supernatural bee. Will Koyomi be able to cure her in time?

Karen is acting clingy and very cute, completely out of character. But its a trick to get Koyomi to introduce her to Kanbaru. In response, he devises a test Karen must pass; a test involving her toothbrush.

Araragi agrees to take Shinobu on a trip to buy doughnuts. At the restaurant, an old acquaintance is able to give information on the town's new visitors.

As Shinobu explains how Tsukihi came to be in her currents situation. Araragi resolves to stop the out-of-towners from killing her. But unlike Oshino and Kaiki, Kagenui speaks with her fist and she talks a lot.

A recap episode retalling the events of Bakemonogatari's Tsubasa Cat and the entirety of Nisemonogatari, narrated by Koyomi. During the summer vacation after all the apparition-related incidents around the five girls have been resolved, Koyomi Araragi's two risky younger sisters – the self-proclaimed heroes of justice, Karen and Tsukihi – become involved in some trouble.

Koyomi finishes hearing the story about 400 years ago from Shinobu. Yotsugi joins them at the spot, and Mayoi wakes up from her slumber. The four of them were talking within the cram school ruins, but the “darkness” appears a second time at that location.

After the graduation of Araragi and Senjougahara, Suruga alone to deal with her left hand that has been turned monsterous from her mother's monkey paw charm. After hearing rumors of a "Devil" that can solve one's problems no matter what, Suruga set out to find this person.

After having her hand healed, Suruga has many questions for her former classmate Rouka. She was unable to contact her, however a meeting with Keiki Deshu, who seems to have survived the attack from the previous season, answers some questions of hers.

Suruga realizes that the collector is in fact Rouka, and she has been collecting parts of the "devil" as she feeds off the misfortune of others. Her motives are questionable...

Rouka challenges Suruga to a one-on-one basketball match as the two discuss the events that led up to their collection of their respective "devil" parts. Suruga is still coming to terms with the ability to use her left arm again.

Upon finding the Demon's head, she meets Rouka once again. Instead of giving the head to Rouka, she refuses. She is unable to stand the sight of her because of the fact that she can see her as she is a ghost. Suruga then challenges Rouka to one-on-one basketball in a wager for the head if Suruga loses.

Koyomi Araragi and Shinobu Oshino discuss the true nature of Shikigami doll Yotsugi Ononoki, and Koyomi is being rudely woken up by his sisters who tell him to cram for his upcoming college entrance exams.

Koyomi Araragi sees that he has no reflection, and discusses this with Shinobu. She then suggests that Koyomi should see Yozuru Kagenui and Yotsugi Ononoki.

When Yotsugi tells Koyomi that he is indeed becoming a vampire, Koyomi reasons that using his vampiric powers must have come with a price. Yozuru tells him that while there is no way to undo the progress of his transformation, there is a way he can stop it from progressing further: he must no longer use his powers as a vampire. However, this turns out to be quite a challenge when he learns his sisters and Suraga have been kidnapped.

Koyomi and Yotsugi land at the base of the mountain, where they are surprisingly met by Ougi Oshino. She talks with Koyomi for a while about his current situation and his upcoming confrontation with Teori. Koyomi and Yotsugi begin their journey up the mountain.

Koyomi attempts to make sense of the mirror world with this world's counterparts of his acquaintances. Later at night, Yotsugi then takes Koyomi to meet yet another person from this world.

Shinobu and Suicide-Master reunited for the first time in 600 years. In contrast to the two rejoicing at their reunion, Izuko delivers some news to Koyomi.