After high school, Koyomi Araragi's story ended. However, the stories of the girls he saved continued, serving as prequels or sequels to their youthful struggles.
Yotsugi Ononoki infiltrates the Araragi residence to monitor Tsukihi Araragi. With Tsukihi at school, Yotsugi spends time freely until she's discovered by the unexpectedly returning Tsukihi.