School Youkai Traveler's Guide (学校妖怪紀行 ~葉~, Gakkou Youkai Kikou: You) is a light novel and one-shot manga written by Ryukishi07 and illustrated by Izumi Rei. It is considered the first iteration of what would go on to become Higanbana no Saku Yoru ni.
Marie Moriya is studying in a classroom when she is unexpectedly greeted by a mysterious girl. The girl begins talking of the "seven wonders" of their school and muses that there is an eighth wonder, a youkai living in an old school bathroom named Mesomeso-san. Though Marie says that she isn't interested in such stories, the mysterious girl pulls her away and guides her towards Mesomeso's bathroom. The girl reveals her name to be Odoru Higanbana.