When Kouichi Sakakibara transfers to his new school, he can sense something frightening in the atmosphere of his new class, a secret none of them will talk about. At the center is the beautiful girl Mei Misaki. Kouichi is immediately drawn to her mysterious aura, but then he begins to realize that no one else in the class is aware of her presence.

[Source: Anime News Network]

Set before the beginning of the story, called the "0th episode" and also "The Other". The OVA shows the stories between Mei Misaki and her twin, Misaki Fujioka, sometime prior to the start of the anime.

[Source: Another Wiki]