すらっぷスティック

When he was a student, Seiji Hibiki had a younger sister, Saori, who died because of a serious disease. Heartbroken, he left his city to study abroad.
Years later, he comes back as a teacher in training. In a new catholic school he discovers that one of his students is his cousin SAORI, who looks exactly like his deceased younger sister. They even have the same name, written with different kanjis.
He meets another student, Kiriko, who dislikes him because of something that happened between him and her mother, the widow KIRIKO. (same name, different kanjis)
One day he meets the funny nun Maria, too, and at night he's stalked by a strange miko girl, MARIA.
What mystery these strange girls are hiding?