Ogata's Sokichi is mercilessly harangued by Iwashita's Oume, and when the added stress of simply caring for three children becomes too much, the pair develop a horrible plan to permanently rid themselves of their perceived new burden.
As the title character, Ogata is not simply an entirely evil man, but instead an emotionally torn whipped dog to Iwashita's icy harridan, but their actions together are still brutally cold and horrific.
Ogata, however, delivers an intensely agitated performance as the confused Sokichi, and Nomura builds to an appropriate payoff that is grounded enough to know that in a story like this, there can never really be a happy ending.
It's a cruel twist of fate that the generation of Japanese filmmakers who survived World War II are dying off just as they are finally beginning to step out of the shadows of the titans of Japanese cinema.
KenOgata is superb in the lead role (I guess he's the demon of the title, but a more pathetic demon you will not find); his performance here reminds me a lot of the serial killer he played in Vengeance is Mine.
The two major set pieces in the movie consist of Ogata taking his daughter (the middle child) to the top of the Tokyo tower, and abandoning her there, and taking his son (the oldest) to the north of Japan with the intention of throwing him off a cliff into the sea.