Monogatari Series: Off & Monster Season Episode 1 SUB at Gogoanime

Synopsis: Yotsugi Ononoki has been infiltrating the Araragi residence to keep an eye on Tsukihi Araragi. While Tsukihi is at school, Yotsugi freely spends her time, but she is seen by Tsukihi, who suddenly comes back home. (Source; Crunchyroll)