Thanks to the (partial, in this case) animation style lifted directly from the much more popular Inferno Cop (both from the same studio), many might think of this anime as a similarly absurd rehash, which is very wrong. Unlike Inferno Cop, Ninja Slayer plays itself completely straight from beginning to end, despite feeling like a parody all the time, with its absurdity being perfectly natural with only one extremely amazing fourth wall break through the whole thing. The action and humor are pretty solid, and so is the incredibly gratuitous fanservice, which borders on parody levels sometimes. Which it does, at least once. The story and characters are solid, and the principal animation is consistently stunning as well, which means the money saved from having characters fighting mostly as static frames was put to good use. The soundtrack is also phenomenal, with a really good OP theme and 26 different ED themes by various artists.
Ninja Slayer is a parody and love letter of some kind to many 80's and 90's action movies and anime, and despite what it looks like from a glance, it's an extremely solid action anime worth tons of fun.
