Sukami Kyouichi was born into an exorcist family, and his older sister is an expert exorcist. She's been putting together a notebook where she has written how to handle all of the different monsters she's met in her work. One day, Kyouichi and his friends in the Occult Club at school go to investigate a supposedly cursed shrine, and he ends up needing to be rescued by his sister. Shortly afterward, she goes missing, presumed by many to be dead, and leaves her little brother with only the notebook.
Kyouichi stays in the Occult club, and as he grows up, he remains dedicated to the search for his beloved older sister. One day, his search starts to finally make some progress, when a shinigami who claims she was his sister's friend appears...

(Source: MangaHelpers)