This movie was "inspired by true events" known as the "Saitama serial murders of dog lovers"; the convicted killers in the real-life case are Gen Sekine (b. January 2, 1942) and his ex-wife Hiroko Kazama (b. February 19, 1957).
This movie is part of the "Hate" trilogy consisting of - Love Exposure, Cold Fish & Guilty of Romance, though these movies are actually NOT connected story-wise.