Koyomi Araragi has finally graduated from high school in Zoku Owarimonogatari, but is this the end of the strange experiences? After the graduation ceremony, he gets a sense of emptiness. Hardly, as Koyomi is immediately pulled in by the mirror as he muses on his future existence in front of it. Some things appear to have altered when he regains consciousness. For instance, his older sister Karen suddenly appears more smaller than usual, and Yotsugi, who often maintains a neutral countenance, seems nearly human. Additionally: The irate Koyomi visits the Kitashirahebi shrine in search of explanations, but en there he frequently gets lost because everyone seems so unlike.
This also applies to Mayoi, who has been chosen to serve as the shrine's new deity, is older-looking, and tells Koyomi that he must have gotten lost in the mirror world and that the only way to get back is for Shinobu to let him via a portal from his world. Together, Koyomi and Yotsugi set out to uncover a way to interact with the other world, but they soon learn that not only is this world filled with unique hazards, but that it also poses risks to them.
