Can't Stop Cursing You誰かを呪わずにいられないこの世界で; Dareka wo Norowazu ni Irarenai Kono Sekai de; This World Needs to be Cursed

At first, it seemed like an ordinary day at Yami High. But it wasn't. A ringing cell phone and the splatter of blood marked the beginning of a deadly game. The rules: Contractor Mikiya has thirty days to curse-kill thirty people or meet a fate worse than death. On the other side, Curse-Breaker Saeyama must identify the killer without falling prey to one of Mikiya's curse-kills. Only time will tell who will emerge victorious.