Natsume Yujin-cho Season 3 Episode 10

An event in the forest causes Tanuma to avoid Natsume the following days, which he becomes concerned about. Mirrors are mysteriously breaking around the school and one day Natsume catches Tanuma acting weirdly. It turns out that Tanuma has been possessed by a youkai looking for her mirror, which had been broken into pieces during a storm a few days before. Using him as a vessel until she reclaims her mirror, Natsume has no choice but to help her. The youkai warns that there may be others seeking the mirror.