Ninja Slayer is a novel series styled as a work by American authors Bradley Bond and Philip "Ninj@" Morzez, who have authorized Honda Yu and Sugi Leika to translate it into Japanese. Enterbrain published the first Japanese version in September 2012, with illustrations by Warainaku. Sixteen novels have been released as of June 2016. It has received three manga adaptations. An ONA adaptation was produced by Trigger and directed by Akira Amemiya which aired from April to October 2015.