Youkai Seishun Hakusho

is a Japanese light novel series written by Masashi Okita, with illustrations by Nukomasu. The series began publication on November 9, 2013 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
In such a modern age where humans become youkai-formerly a perfect handsome boy → But now Yukio-kun has become a fluffy wild man.

From his appearance, his worries are that no matter how cool he says or acts, he becomes comical. And, in the old days, a well-behaved innocent girl → But now Kaoruko-san has become a cute snake girl who loves off-color humor. She loves Yukio, and it's worth playing with Yukio. In terms of spirituality, motivation, and sexuality !?

A pure and impure youkai cohabitation romantic comedy that spells out the smiley, off-color humor of these two people!