The history of the word hentai has its origins in science and psychology.
By the middle of the Meiji era, the term appeared in publications to describe unusual or abnormal traits, including paranormal abilities and psychological disorders. A translation of German sexologist Richard von Krafft-Ebing's text Psychopathia Sexualis originated the concept of hentai seiyoku, as a 'perverse or abnormal sexual desire', though it was popularized outside psychology, as in the case of Mori Ōgai's 1909 novel Vita Sexualis.
Continued interest in hentai seiyoku resulted in numerous journals and publications on sexual advice which circulated in the public, served to establish the sexual connotation of hentai as perverse.
