text: Yōkai have been collected and categorized for thousands of years. An ancient legend tells of an encyclopedia called The Book of the Hakutaku, which was given to the emperor by a magical beast. This book contained information about all the spirits, gods, and demons in the universe.
  
  It was lost long ago, but parts of it were copied down. People have been collecting information about the spirit world in supernatural encyclopedias ever since. Nowhere was this tradition of collecting yōkai more passionate and widespread than in Japan.
  
  While yōkai are antique, the majority of them were not invented until the 16th century and onwards. In ancient times, yōkai were imagined as invisible, malevolent forces lacking physical form. The most popular legends involved oni (demons) and onyrō (vengeful ghosts). This changed during the Muromachi Period with the arrival of a series of picture scrolls depicting the night parade of one hundred demons. In this long procession, grotesque and comical monsters cavort and dance from sunset to sunrise. The earliest picture scrolls did not include names or stories to accompany the creatures. Some of them were recognizable as ghosts from popular Heian Period classics. Others were household objects with comical human-like features—a type of yōkai known as tsukumogami. These depictions of hordes of strange monsters laid the foundation for a massive yōkai boom in the coming centuries.
  
  During the Edo Period, artists copied the picture scrolls, adding new yōkai to the parade. They gave names and invented stories for the creatures. The flourishing economy and new technologies allowed for the mass production of illustrated books. Demand for cheap reading material was high. Artists like Toriyama Sekien collected yōkai from around the country and bundled them into illustrated, multi-volume encyclopedias. As demand for yōkai grew, artists looked back into Japanese literature and history for inspiration. They copied monsters from ancient Chinese classics, reinterpreting them through a Japanese lens. They even invented new yōkai based on puns and reflecting contemporary societal issues.
  
  When the Edo Period ended, Japan began to modernize rapidly. Belief in yōkai quickly faded away as scientific discoveries began to explain away the mysteries of the past. However, the appeal of yōkai remained strong. Folklorists like Inoe Enryō and Yanagita Kunio collected folk tales and superstitions from around the country. The cartoonist Mizuki Shigeru further helped save yōkai from disappearing by bringing them to pop culture and reintroducing them to the post-war world. Like those before him, he collected his yōkai in illustrated encyclopedias, and tried to document as much of Japan's folklore as he could.
  
  Today, the appeal of yōkai remains strong. Universities preserve and present yōkai in vast searchable folklore databases—a sort of online Book of the Hakutaku. Thanks to the internet, yōkai have become accessible to people all over the world. And the ancient tradition of collecting them continues today in the form of collectible card games, video games, television, movies—and of course books like this one.