Denpa-teki na Kanojo is one of hollowest work of anime i have ever watched to the point that i was pretty sure this was a troll show made deliberately to be absolute trash and i feel like idiot for falling for low level bait.
moving on , this show is listed as mystery thriller, school although it should say "complete dumpster trash".
Listen show then cast consists of 4 characters and 2 are protagonists and one is killed, its doesnt take collective deducing power of L, Sherlock and every detective in existence to guess who murder might fucking be.
thriller , well yes if in about 40 minutes of watching there are bout 2 frames showing dead bodies counts as thriller . So you not going to be getting any juvenile violence to entertain you.
ah yes school . Well school part is just excuse to have characters be high schoolers and so that sho can go "booooh look at this high schoolers being guilty and making yandere faces booohh so scaaary'
I'll be frank unless your 6 or your definition of horror includes shitily edited ghost videos from 2010 youtube, this show is one of laziest works of fiction you will come across and I advise to go watch something else like Shiki
