Ghost Stories/Gakkou no Kaidan (Dubbed) S1/E9

Satsuki's school pet keeper, Mio, brings a rabbit, Shirotabi, back to life through a black magic ritual. The spell works, but with a side-effect, Shirotabi gets cursed and turns into a demon every night. Although Mio tries to stop Shirotabi, she realizes Shirotabi no longer even recognizes her. Satsuki and the others to convince Mio that Shirotabi's place should be with the dead, and Mio agrees. Mio breaks the spell, and Shirotabi is released from the curse