Student Number Zero

Io Sado, a second-year junior high school student who loves the occult, encounters a mysterious teenager called "Student number 0", who is present in the classroom but never noticed by anyone. Io had an occult experience of having a fun school life with number 0 and drifting to another world where strange monsters appeared. Through such an experience, she develops a "certain feeling" towards Number 0...? The youth occult battle begins!!