[Request] Violent Horror/Thrillers?

I loved Higurashi No Naku Koro Ni, but I was put off by the end twist. [Spoilers.](/s Insert "aliens" meme here) I hate that kind of thing; it felt like too lazy of an explanation. Though I watched it a number of years ago, a few of the arcs stick with me- mostly the ones where everyone slowly goes batshit insane and the MC is the only one to stay really sane. I'm looking for something along those lines without the [spoiler](/s aliens) crap.

I tried School Days, but it wasn't quite there. I would like, if possible, for the big reveal to be at the very end if it happens at all. With School Days, though, the action took too long to mount. If it's JUST a thriller series that ends without a reveal and leaves me unfulfilled or depressed, that's perfect.

Bonus points for an anime 12 or less episodes with multiple series (Higurashi Ni, Kai, etc). Perhaps I'm being too specific? If there are any questions, I can answer in the comments. I do not have a MAL.

If it turns out that the other Higurashi series are what I'm looking for, let me know. I'd just like to go without an [spoiler.](/s "aliens" reveal.)

Quick edit: I should mention that I LOVED the last episode of School Days, though I wasn't satisfied with most of the rest of the series.

Edit 2: I just remembered to mention that I loved Mirai Nikki, as well!