Kiben Gakuha, Yotsuya-senpai no Kaidan.

In the midst of a female-kidnapping serial killer incident, Makoto's best friend Hinano has vanished completely. Desperate to find her before it's too late, Makoto will try anything-- even invoking the resident phantom student of her middle school, Yotsuya-senpai!

Surprisingly, Yotsuya-senpai appears to be an actual person. He's obsessed with creating the scariest stories ever, using the people and situations in Makoto's middle school to stage them. Though Yotsuya is mostly just interested making scary stories, Makoto finds that his stories tend to contain a kernel of truth and that they can reveal their terrible truth in the telling. But as Makoto helps Yotsuya stage his tales, can she convince him to tell the story of the whereabouts of her best friend?

(Source: MangaHelpers)

Included one-shots:
Volume 2: Asobiba.
Volume 3: Ousama Kid; Kiben Gakuha, Yotsuya-sensei no Kaidan (pilot)