Anime Happy-Tree Friends. Literally all you need to know. Take the familiar formula of cute chibi 2 dimensional characters on a flat background that may very well have been drawn in Microsoft Paint, inject it with ultra-violence with no consequences or permanence, and then thrown in a handful of anime tropes and bingo-bango you've got Ao Oni. They are a quick watch but fairly entertaining in a Ebaum's World or Newgrounds kind of way. You probably won't be declaring it a masterpiece, but it may elicit a chuckle from sheer absurdity.
Also it is tagged as "horror." This seems inaccurate. The original medium was a game that i gather was a horror game, but this animated adaptation seems to have gone in a completely different direction I guess if were taken seriously for a single second the subject matter could be considered horrific, but the whole thing is nothing more than a series of slapstick gags. It is absolutely intended to be viewed as a comedy.