aku_no_monogatari
Light novel duology by mothy. A loosely connected spin-off of Evillious Nendaiki set after master of the heavenly yard (vocaloid). The first novel is Aku no Monogatari: Kami no Akuma to Himitsu no Shoko, and its sequel is Aku no Monogatari: Tasogare no Akuma to Nisemono no Joou.
Not to be confused with Aku no Musume (series).