MC's father, who was living (without him) with MC's cousins for the last years, just died, and MC is passing a few days with those cousins (4 sisters).
He has strange dreams of becoming some monster and killing people, and it turns out those dreams were real.
It turns out his family has oni blood, and in the males it eventually becomes too strong to be controlled, so the eldest of the sisters, the family head, has decided to kill MC before he has to suffer that.
But it also turns out that it wasn't him who was doing the murders, but another person who also could turn into an oni and with whom for some reason (if there's an explanation I haven't reached it yet) MC had a link so could see while sleeping what the other was doing.