Oh!! My Master

A boy's ghost possesses a school girl because he has unfinished business in the world of the living. He says he needs to have sex before he can rest in peace, and she's the only one who can see him. She's an unwilling host, especially since sex with another girl would ruin her reputation at school.

Note: This story is actually later in the manga under the title 彼と私の恋愛法.