Gakuen Benriya Series: AntiqueHeart

Synopsis (en anglais)

There's an old decrepit building at the edge of the school grounds that hasn't been used for years, and it falls apart a little bit more each day. But the little house holds a secret, as Takahiro and his friends are soon to find out...they wind up making contact with a mysterious entity known as Saki. Can Takahiro save Saki's world from destruction. (Source: Anime News Network)