One of my personal favorite genres, horror is everything that we as humans fear, are anxious of, or grossed out by. There are many sub-genres of horror, such as suspense, which is simply the fear of the unknown or out of sight; we tell ourselves something is there, but we can’t be sure, nor do we know when it’ll pop out at us. Bizarre looking monsters that are the things of nightmares, blood and gore, or death in general are common tropes used in horror anime and manga.
Unfortunately, while there are some fantastic works of horror fiction, most that come to surface aren’t very well written/illustrated, and overall I feel that the genre is underappreciated.