What is "yokaiden"

Yōkaiden is an ongoing Original English-language manga written and illustrated by Nina Matsumoto and published by Del Rey Manga. The story features Hamachi, a boy fascinated by the Japanese monsters called yokai. When one of these monsters steals his grandmother's soul, he travels into their world to retrieve it. The first volume was published on November 18, 2008, and as of November 24, 2009, two volumes were released.