Calamity/curse is chasing a particular middle school class for decades, taking lives of students and their family members in non-supernational accidents, roughly one person per month, unless "countermeasures" work.
Newly arrived student notices an "invisible" student who don't interact with anybody and whom everybody pretend to not exist.
Slowly developing show where in first half of the series protagonist struggles for anybody to explain to him what is going on, although surprisingly we later learn a good reason for that.
Average story is about how easy it is to lose sanity to fear, and act irrationally and violently, individually or in masses. It is hardly surprising that the show ends with gore-fest...
https://myanimelist.net/anime/11111/Another
