The five girls' problems with supernatural beings have been solved, and it's now summer break, with the culture fair over. Koyomi Araragi has two little sisters, self-proclaimed "heroes" nicknamed the Fire Sisters, Karen and Tsukihi.

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

While taking Karen to meet Kanbaru, Araragi is put into a compromising position. On the way, he runs into someone asking about familiar things.

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.

Nadeko spent the evening at the Araragi residence after Koyomi mistakes her for running away from home and takes her back to his place. The next morning, she talks to Koyomi's younger sister Tsukihi, a friend from back in grade school.

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.